Application method for improving methanol combustion efficiency in medium-speed diesel and methanol dual-fuel engine

Abstract

The invention provides an application method for improving methanol combustion efficiency in a medium-speed diesel and methanol dual-fuel engine, and relates to the field of engine combustion technologies and alternative fuels. 2, an air inlet system is transformed; step 3, performing a dual-mode control strategy; 4, load self-adaptive adjustment is carried out; 5, the combustion efficiency is improved, and the problems that the calorific value of methanol is less than half of that of diesel oil, the volume calorific value is low, and if an existing diesel oil injection system is directly used, the engine power is greatly reduced are solved; the diesel oil injection performance is deteriorated by simply increasing the injection quantity; in addition, when the air inlet channel is used for spraying the methanol, the problem of methanol knocking easily occurs, and the substitution rate of the methanol is limited is solved.

Description

Technical Field

[0001] This invention relates to the fields of engine combustion technology and alternative fuel technology, and in particular to a method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine. Background Technology

[0002] With increasing global emphasis on environmental protection and sustainable development, traditional diesel engines are facing increasingly stringent emission regulations. Diesel combustion produces large amounts of pollutants such as nitrogen oxides and particulate matter, which seriously harm the environment and human health. At the same time, the increasing scarcity of petroleum resources is prompting people to seek alternative fuels to meet energy demands.

[0003] Methanol can be produced through various pathways, such as from raw materials like coal, natural gas, and biomass, making it a relatively abundant source that can alleviate dependence on petroleum resources to some extent. The combustion of methanol produces relatively few pollutants, especially low levels of sulfur and particulate matter, which helps reduce air pollution and greenhouse gas emissions, meeting environmental protection requirements. Furthermore, if methanol is produced using renewable resources, its entire life cycle can achieve carbon neutrality, making it a promising low-carbon fuel.

[0004] Medium-speed engines are widely used in ships, power generation and other fields, and have high requirements for engine power performance, reliability and economy; introducing methanol into diesel engines to form dual-fuel engines can reduce operating costs and emissions while ensuring power output.

[0005] However, methanol and diesel have significantly different combustion characteristics. For example, methanol has a calorific value of less than half that of diesel and a lower volumetric calorific value. If existing diesel injection systems are used directly, engine power will be greatly reduced. Simply increasing the injection volume will lead to a deterioration in diesel injection performance. In addition, methanol knocking is prone to occur when methanol is injected through the intake manifold, which limits the substitution rate of methanol.

[0006] To address these issues, researchers have conducted extensive research on medium-speed diesel-methanol dual-fuel engines. For example, by optimizing the engine's combustion and fuel injection systems, and employing advanced electronic control technology to precisely control the injection quantity, timing, and ratio of methanol and diesel, they aim to achieve efficient combustion and good performance matching. Simultaneously, they are continuously exploring new combustion modes and control strategies, such as homogeneous charge compression ignition (HCCI) and low-temperature combustion, to further improve methanol combustion efficiency and overall engine performance. However, some technical challenges remain to be addressed, such as the combustion stability of methanol under different operating conditions and its compatibility with engine component materials.

[0007] In conclusion, improving methanol combustion efficiency in medium-speed diesel-methanol dual-fuel engines has significant practical implications, and related research plays an important role in promoting engine technology development and meeting environmental and energy demands. Summary of the Invention

[0008] In view of this, the present invention provides a method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine, which includes the following steps:

[0009] Step 1: Methanol Injection Timing Optimization: Adjust the methanol injection timing to the intake top dead center (TDC) at 0°. This injection timing ensures that the crankshaft angle accuracy is controlled within ±0.5°, and the overlap angle α formed by the methanol injection start point and the exhaust valve closing point satisfies the formula: α=θ inj -θ evc Where α is the overlap angle, measured in °CA (crankshaft angle), used to measure the degree of time overlap between methanol injection and exhaust valve closure; θ inj θ represents the methanol injection initiation angle, in °CABTDC, and the crankshaft rotation angle before top dead center, indicating the angle of the crankshaft relative to top dead center when methanol injection begins; evc The exhaust valve closing angle is expressed in °CABTDC, which is the angle of the crankshaft relative to the top dead center when the exhaust valve is closed. α must be within the range of 5° to 15° to ensure good heat exchange conditions.

[0010] Step 2: Intake System Modification: Install a venting device in the main unit's intake chamber. The venting device includes an electric actuator, a flow regulating valve, and a pressure sensor. The valve's flow capacity is C. v Satisfying the formula: Among them, C v The flow capacity of a valve is an important parameter for measuring its flow characteristics; Q represents the gas flow rate, measured in cubic meters per second (m³). 3 / h refers to the gas volume flow rate through the valve; ΔP is the pressure difference across the valve, in bar, reflecting the pressure change across the valve; ρ 20 The density of air at 20℃ is expressed in kg / m³. 3 ρ is the standard reference density; ρ is the actual gas density under operating conditions, in kg / m³. 3 It varies due to factors such as temperature and pressure during actual operation;

[0011] Step 3: Dual-mode control strategy: When the main unit is running in diesel mode, the venting device valve is closed. At this time, the oxygen concentration (O2%) in the intake chamber satisfies the formula:

[0012] Wherein, O2% is the percentage of oxygen concentration in the intake chamber; V airThe volume of air entering the intake chamber, expressed in m³. 3 ; 0.21 is the volume percentage of oxygen in the air; V res The volume of residual gas in the intake chamber, in cubic meters (m³). 3 This formula is used to calculate the oxygen concentration in the intake chamber, which needs to be maintained within the range of 20.5% to 21% to ensure complete combustion of diesel fuel.

[0013] Step 4: Load Adaptive Adjustment: Based on the intake pressure Pin (bar) and exhaust temperature Texh (°C) of the main unit under different loads L (%), the opening amplitude Cv of the vent valve is controlled by PID control. The control algorithm satisfies:

[0014] Among them, C v (t) represents the opening degree of the vent valve at time t; K p K is the proportional coefficient used to quickly address the deviation. i K is the integral coefficient, used to eliminate steady-state error; d is the differential coefficient, which predicts the trend of deviation change; e(t) is the deviation between the setpoint SP and the actual load L(t); The integral term of the error. K is the differential term of the error; at 25% load, K p =0.8, K i =0.02, K d =0.1, these parameters determine the adjustment effect of valve opening;

[0015] Step 5: Improve combustion efficiency: By adjusting the timing of methanol injection and the combined effect of intake and exhaust, the compensation amount Q of the latent heat of methanol vaporization is increased. comp Satisfying the formula: Q comp =m meoh ·ΔH v ·η heat

[0016] (where Q) comp This is the compensation amount for the latent heat of methanol vaporization, expressed in kJ, used to measure the heat required to supplement methanol vaporization; m meoh The mass of methanol is expressed in kg; ΔH v The latent heat of methanol vaporization, with a value of 1109 kJ / kg, represents the heat absorbed during the methanol vaporization process; η heat Heat exchange efficiency (reflecting the effectiveness of heat transfer), and η heat Calculated using the exhaust waste heat recovery coefficient φ and the intake air temperature rise coefficient γ:

[0017] in, To optimize the intake air temperature, the unit is K; To optimize the front airflow temperature, the unit is K; c p Specific heat capacity of air, unit: kJ / kg·K; m air Q represents air mass flow rate, expressed in kg / s. exh φ represents the exhaust heat, expressed in kJ / s; φ is the exhaust waste heat recovery coefficient, ranging from 0.35 to 0.45, used to measure the degree of exhaust waste heat recovery and utilization.

[0018] Furthermore, in step 2, the valve opening C of the venting device... v With engine load L and intake pressure P in Exhaust temperature T exh The relationship satisfies the three-dimensional mapping function: C v =f(L,P in ,T exh )=a0+a1L+a2P in +a3T exh +a4LP in +a5LT exh +a6P in T exh +a7LP in T exh , where C v P represents the vent valve opening; L represents the engine load, expressed as a percentage; P represents the vent valve opening. in T represents intake pressure, measured in bar. exh The exhaust temperature is expressed in °C; a0, a1, a2, a3, a4, a5, a6, and a7 are function coefficients, with values ​​of 12.5, 0.85, 15.2, 0.12, 0.03, 0.0015, 0.002, and 0.00005, respectively.

[0019] Furthermore, in step 4, the valve opening C under different loads... v The following relationship exists between the intake pressure drop ΔPin and the exhaust temperature rise ΔTexh:

[0020] 25% load:

[0021] 50% load:

[0022] 75% load:

[0023] 100% load:

[0024] Among them, C v Valve opening, expressed as a percentage; ΔP inΔT represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. exh This represents the increase in exhaust temperature, expressed in °C, reflecting the change in exhaust temperature after valve opening adjustment.

[0025] Furthermore, in step 5, the increase in methanol substitution rate Rmeoh and the increase in exhaust temperature ΔTexh satisfy an exponential relationship:

[0026] Where, ΔR meoh R0 represents the increase in methanol substitution rate, used to measure the degree of increase in the proportion of diesel replaced by methanol; R0 is the maximum substitution rate increase potential, with a value of 12%; λ is the temperature sensitivity coefficient, with a value of 0.025℃. -1 ΔT reflects the degree to which changes in exhaust temperature affect the methanol substitution rate; exh This represents the increase in exhaust temperature, expressed in °C, and this relationship exists over ΔT. exh When the temperature is between 20℃ and 60℃, the error shall not exceed ±1.2%.

[0027] Furthermore, the adaptive adjustment of the PID control parameters in step 4 satisfies the Ziegler-Nichols method:

[0028] proportionality coefficient K p :

[0029] Integral coefficient K i :

[0030] Differential coefficient K d :

[0031] Among them, K p K i K d These are the proportional, integral, and derivative coefficients for PID control; K u The critical gain is the proportional gain of the system when it is in a critical steady state; T u The critical oscillation period is the oscillation period of the system when it is in a critical steady state; L is the engine load, expressed as a percentage. These formulas are used to adaptively adjust the PID control parameters according to the engine load.

[0032] Furthermore, the switching process between diesel mode and methanol dual-fuel mode in step 3 satisfies the following timing control:

[0033] Diesel → Dual-fuel switch:

[0034] Among them, t transt0 is the switching time from diesel mode to dual-fuel mode, in seconds; t0 is the start-up time, in seconds; V pipe This refers to the intake manifold volume, measured in cubic meters (m³). 3 Q air Airflow rate, unit: m³ / s 3 / s; τ is a time constant with a value of 5s. This formula is used to calculate the time required for mode switching.

[0035] Dual-fuel to diesel switching:

[0036] Among them, t purge The purging time for switching from dual-fuel mode to diesel mode, in seconds; V cyl Total cylinder volume, in cubic meters (m³). 3 n is the engine speed, in rpm; Δt is the time of a single cycle, in seconds; V stroke The stroke volume is expressed in cubic meters (m³). 3 This formula is used to determine the purging time when switching modes to remove residual methanol gas;

[0037] Furthermore, the silencing device of the venting device in step 2 adopts an impedance composite structure, and its noise reduction NR satisfies: NR = NR res +NR abs ;

[0038] Wherein, NR represents the total noise reduction of the silencing device, measured in dB; NR res This refers to resonant noise reduction, measured in dB, which eliminates noise at specific frequencies through the principle of resonance; NR abs The resistive noise reduction is expressed in dB (using sound-absorbing materials to absorb noise energy), and:

[0039]

[0040] Where f is the sound wave frequency in Hz; f0 is the resonant frequency in Hz; and ρ is the air density in kg / m³. 3 c is the speed of sound, in m / s; S is the cross-sectional area of ​​the channel, in m². 2 R is the acoustic resistance; α is the sound absorption coefficient; L is the silencer length in meters; P is the channel circumference in meters. These parameters are used to calculate the resonant silencing and resistive silencing.

[0041] Furthermore, in step 4, when the intake pressure drops beyond a preset safety threshold ΔP... safe When the host protection system is triggered, the security threshold is met: Where, ΔP safe This is a preset safety threshold, in bar; P minMinimum allowable intake pressure, measured in bar, is the minimum intake pressure required to ensure normal engine operation. The nominal intake pressure, in bar, is the standard intake pressure under normal engine operating conditions, and ΔP safe Calculated dynamically using the following formula: Where L is the engine load, expressed as a percentage, and the formula dynamically adjusts the safety threshold based on the engine load.

[0042] Furthermore, after the combustion efficiency is improved in step 5, the engine thermal efficiency η th satisfy: Where, η th To improve engine thermal efficiency after combustion efficiency; The original thermal efficiency; Δη meoh Improved thermal efficiency resulting from improved methanol combustion; Δη heat (The improvement in thermal efficiency brought about by waste heat recovery), and: (where Δη) meoh In the middle, m meoh Q is the methanol mass flow rate, expressed in kg / s. LHV,meoh The lower heating value of methanol is 19.9 MJ / kg; η comb,meoh The methanol combustion efficiency is 98%; P out Output power, in kW; Δη heat In this context, Qrec represents the recovered heat, measured in kW; η rankine For the Rankine cycle efficiency, the value is 12%. These formulas are used to calculate the increase in thermal efficiency due to methanol combustion and waste heat recovery.

[0043] Furthermore, in step 4, the optimal control curves for valve opening under different loads are obtained through genetic algorithm optimization, with the objective function being: Among them, F(C v Let C be the objective function value. The optimal valve opening C is determined by minimizing this value through optimization. v ;ΔR meoh The increase in methanol substitution rate, ΔR, is used to measure the extent to which methanol replaces diesel. meoh The maximum possible substitution rate is set to 12%. The weighting coefficient w1, which reflects the normalization of the methanol substitution rate increase in the objective function, is set to 0.45, indicating the degree of importance attached to increasing the methanol substitution rate; ΔP in P represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. max The maximum allowable intake pressure drop is set to 0.6 bar. To reflect the normalization considerations of the intake pressure reduction in the objective function, w2 is set to 0.25; ΔT exh This represents the increase in exhaust temperature, expressed in degrees Celsius (°C), reflecting the change in exhaust temperature after valve opening adjustment (T). max The maximum permissible exhaust temperature rise is set at 60°C. This represents the normalized weight of the exhaust temperature rise in the objective function, with w3 taking a value of 0.15; NO x The optimized nitrogen oxide emission value, The nitrogen oxide emission values ​​before optimization. The value of w4, representing the proportion of nitrogen oxide emission changes in the objective function, is 0.15, used to balance the importance of emission control in the optimization objective. By iteratively optimizing this objective function using a genetic algorithm, the optimal valve opening C for overall engine performance under different loads can be determined. v Control curve.

[0044] Beneficial effects

[0045] I. The methanol substitution rate has increased significantly, reducing fuel costs and carbon emissions.

[0046] 1. Core Technology: Adjust the methanol injection timing to the top dead center (TDC) of the intake air to 0°, and use exhaust waste heat and intake venting strategies to increase the exhaust temperature (e.g., the exhaust temperature increases by 50°C at 75% load), fully compensating for the latent heat of methanol vaporization and ensuring complete vaporization and combustion of methanol.

[0047] 2. Actual results:

[0048] The methanol substitution rate can be increased by 5% to 10% (e.g., 5% at 25% load and 10% at 75% load).

[0049] Methanol is a renewable energy source that produces no pollutants when burned, aligning with the goal of "carbon reduction" and significantly reducing carbon emissions.

[0050] II. Simultaneous optimization of combustion efficiency and thermal efficiency enhances power economy.

[0051] 1. Core Technology: Optimize the methanol injection timing and intake / exhaust overlap angle, and combine intake and exhaust to increase the cylinder temperature, thereby significantly improving methanol combustion efficiency. At the same time, improve engine thermal efficiency through exhaust waste heat recovery.

[0052] 2. Actual benefits:

[0053] The engine fuel consumption rate is reduced by 58%, and the power output stability is improved, making it suitable for medium-speed operating scenarios such as ships and power generation.

[0054] Improved thermal efficiency reduces energy waste and significantly improves the economic efficiency of main unit operation.

[0055] III. Optimized emission performance to meet stringent environmental standards

[0056] 1. Core Technology: By reducing oxygen content through intake and exhaust, the formation of nitrogen oxides (NOx) at high temperatures is suppressed, resulting in a 15% to 25% reduction in NOx emissions.

[0057] IV. Strong adaptability to all working conditions, improved system stability and safety.

[0058] 1. Operating condition adaptation technology:

[0059] Through dynamic mapping and adaptive control, the valve opening can be precisely adjusted under 25% and 100% load (e.g., 20% opening at 25% load and 40% opening at 100% load), avoiding insufficient air intake or overheating.

[0060] It is compatible with different engine displacements and injection methods, and has a wide range of applications.

[0061] 2. Security protection mechanism:

[0062] Real-time monitoring of intake pressure; in case of abnormality, automatic adjustment of valve opening and switching of fuel mode to prevent unstable combustion.

[0063] V. Waste Heat Recovery and Equipment Life Optimization

[0064] 1. Waste heat utilization: Waste heat recovery from exhaust gas increases the intake air temperature, compensates for the heat absorption during methanol vaporization, and reduces the difficulty of cold start.

[0065] 2. Equipment maintenance: Improved combustion efficiency reduces piston ring wear, extends cylinder liner replacement intervals, reduces carbon buildup on exhaust valves, and lowers maintenance costs.

[0066] VI. Low cost and easy implementation, while taking noise control into account.

[0067] 1. Modification cost: The venting device uses a common ball valve, which has low modification cost, does not require major changes to the main unit structure, and is easy to install.

[0068] 2. Noise control: The silencer effectively reduces noise and meets equipment noise standards.

[0069] By combining injection timing optimization with intake and exhaust control technologies, a complete solution has been formed, encompassing combustion efficiency improvement, emission control, and system safety. This solution offers both economic and environmental benefits in engineering applications and is particularly suitable for energy-saving and carbon-reduction retrofitting of medium-speed diesel-methanol dual-fuel engines. Attached Figure Description

[0070] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below;

[0071] The accompanying drawings described below are only related to some embodiments of the present invention and are not intended to limit the invention.

[0072] In the attached diagram:

[0073] Figure 1 This is a methanol injection timing phase diagram of an embodiment of the present invention for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine. Detailed Implementation

[0074] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples;

[0075] Example: Please refer to Figure 1 As shown:

[0076] This invention provides a method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine, comprising the following steps:

[0077] Step 1: Methanol Injection Timing Optimization: Adjust the methanol injection timing to the intake top dead center (TDC) at 0°. This injection timing ensures that the crankshaft angle accuracy is controlled within ±0.5°, and the overlap angle α formed by the methanol injection start point and the exhaust valve closing point satisfies the formula: α=θ inj -θ evc Where α is the overlap angle, measured in °CA (crankshaft angle), used to measure the degree of time overlap between methanol injection and exhaust valve closure; θ inj θ represents the methanol injection initiation angle, in °CABTDC, and the crankshaft rotation angle before top dead center, indicating the angle of the crankshaft relative to top dead center when methanol injection begins; evc The exhaust valve closing angle is expressed in °CABTDC, which is the angle of the crankshaft relative to the top dead center when the exhaust valve is closed. α must be within the range of 5° to 15° to ensure good heat exchange conditions.

[0078] Step 2: Intake System Modification: Install a venting device in the main unit's intake chamber. The venting device includes an electric actuator, a flow regulating valve, and a pressure sensor. The valve's flow capacity is C. v Satisfying the formula: Among them, C v The flow capacity of a valve is an important parameter for measuring its flow characteristics; Q represents the gas flow rate, measured in cubic meters per second (m³). 3 / h refers to the gas volume flow rate through the valve; ΔP is the pressure difference across the valve, in bar, reflecting the pressure change across the valve; ρ 20 The density of air at 20℃ is expressed in kg / m³. 3 ρ is the standard reference density; ρ is the actual gas density under operating conditions, in kg / m³. 3It varies due to factors such as temperature and pressure during actual operation;

[0079] Step 3: Dual-mode control strategy: When the main unit is running in diesel mode, the venting device valve is closed. At this time, the oxygen concentration (O2%) in the intake chamber satisfies the formula:

[0080] Wherein, O2% is the percentage of oxygen concentration in the intake chamber; V air The volume of air entering the intake chamber, expressed in m³. 3 ; 0.21 is the volume percentage of oxygen in the air; V res The volume of residual gas in the intake chamber, in cubic meters (m³). 3 This formula is used to calculate the oxygen concentration in the intake chamber, which needs to be maintained within the range of 20.5% to 21% to ensure complete combustion of diesel fuel.

[0081] Step 4: Load Adaptive Adjustment: Based on the intake pressure Pin (bar) and exhaust temperature Texh (°C) of the main unit under different loads L (%), the opening amplitude Cv of the vent valve is controlled by PID control. The control algorithm satisfies:

[0082] Among them, C v (t) represents the opening degree of the vent valve at time t; K p K is the proportional coefficient used to quickly address the deviation. i K is the integral coefficient, used to eliminate steady-state error; d is the differential coefficient, which predicts the trend of deviation change; e(t) is the deviation between the setpoint SP and the actual load L(t); The integral term of the error. K is the differential term of the error; at 25% load, K p =0.8, K i =0.02, K d =0.1, these parameters determine the adjustment effect of valve opening;

[0083] Step 5: Improve combustion efficiency: By adjusting the timing of methanol injection and the combined effect of intake and exhaust, the compensation amount Q of the latent heat of methanol vaporization is increased. comp Satisfying the formula: Q comp =m meoh ·ΔH v ·η heat

[0084] (where Q) comp This is the compensation amount for the latent heat of methanol vaporization, expressed in kJ, used to measure the heat required to supplement methanol vaporization; m meoh The mass of methanol is expressed in kg; ΔH vThe latent heat of methanol vaporization, with a value of 1109 kJ / kg, represents the heat absorbed during the methanol vaporization process; η heat Heat exchange efficiency (reflecting the effectiveness of heat transfer), and η heat Calculated using the exhaust waste heat recovery coefficient φ and the intake air temperature rise coefficient γ:

[0085] in, To optimize the intake air temperature, the unit is K; To optimize the front airflow temperature, the unit is K; c p Specific heat capacity of air, unit: kJ / kg·K; m air Q represents air mass flow rate, expressed in kg / s. exh φ represents the exhaust heat, expressed in kJ / s; φ is the exhaust waste heat recovery coefficient, ranging from 0.35 to 0.45, used to measure the degree of exhaust waste heat recovery and utilization.

[0086] In step 2, the valve opening C of the venting device v With engine load L and intake pressure P in Exhaust temperature T exh The relationship satisfies the three-dimensional mapping function: C v =f(L,P in ,T exh )=a0+a1L+a2P in +a3T exh +a4LP in +a5LT exh +a6P in T exh +a7LP in T exh , where C v P represents the vent valve opening; L represents the engine load, expressed as a percentage; P represents the vent valve opening. in T represents intake pressure, measured in bar. exh The exhaust temperature is expressed in °C; a0, a1, a2, a3, a4, a5, a6, and a7 are function coefficients, with values ​​of 12.5, 0.85, 15.2, 0.12, 0.03, 0.0015, 0.002, and 0.00005, respectively.

[0087] In step 4, the valve opening C under different loads v The following relationship exists between the intake pressure drop ΔPin and the exhaust temperature rise ΔTexh:

[0088] 25% load:

[0089] 50% load:

[0090] 75% load:

[0091] 100% load:

[0092] Among them, C v Valve opening, expressed as a percentage; ΔP in ΔT represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. exh This represents the increase in exhaust temperature, expressed in °C, reflecting the change in exhaust temperature after valve opening adjustment.

[0093] In step 5, the increase in methanol substitution rate Rmeoh and the increase in exhaust temperature ΔTexh satisfy an exponential relationship:

[0094] Where, ΔR meoh R0 represents the increase in methanol substitution rate, used to measure the degree of increase in the proportion of diesel replaced by methanol; R0 is the maximum substitution rate increase potential, with a value of 12%; λ is the temperature sensitivity coefficient, with a value of 0.025℃. -1 ΔT reflects the degree to which changes in exhaust temperature affect the methanol substitution rate; exh This represents the increase in exhaust temperature, expressed in °C, and this relationship exists over ΔT. exh When the temperature is between 20℃ and 60℃, the error shall not exceed ±1.2%.

[0095] In step 4, the adaptive adjustment of the PID control parameters satisfies the Ziegler-Nichols method:

[0096] proportionality coefficient K p :

[0097] Integral coefficient K i :

[0098] Differential coefficient K d :

[0099] (where K) p K i K d These are the proportional, integral, and derivative coefficients for PID control; K u The critical gain is the proportional gain of the system when it is in a critical steady state; T u The critical oscillation period is the oscillation period of the system when it is in a critical steady state; L is the engine load, expressed as a percentage. These formulas are used to adaptively adjust the PID control parameters according to the engine load.

[0100] In step 3, the switching process between diesel mode and methanol dual-fuel mode satisfies the following timing control:

[0101] Diesel → Dual-fuel switch:

[0102] Among them, t trans t0 is the switching time from diesel mode to dual-fuel mode, in seconds; t0 is the start-up time, in seconds; V pipe This refers to the intake manifold volume, measured in cubic meters (m³). 3 Q air Airflow rate, unit: m³ / s 3 / s; τ is a time constant with a value of 5s. This formula is used to calculate the time required for mode switching.

[0103] Dual-fuel to diesel switching:

[0104] Among them, t purge The purging time for switching from dual-fuel mode to diesel mode, in seconds; V cyl Total cylinder volume, in cubic meters (m³). 3 n is the engine speed, in rpm; Δt is the time of a single cycle, in seconds; V stroke The stroke volume is expressed in cubic meters (m³). 3 This formula is used to determine the purging time when switching modes to remove residual methanol gas.

[0105] In step 2, the silencing device of the venting device adopts an impedance composite structure, and its noise reduction NR satisfies: NR = NR res +NR abs ;

[0106] Wherein, NR represents the total noise reduction of the silencing device, measured in dB; NR res This refers to resonant noise reduction, measured in dB, which eliminates noise at specific frequencies through the principle of resonance; NR abs The resistive noise reduction is expressed in dB (using sound-absorbing materials to absorb noise energy), and:

[0107]

[0108] Where f is the sound wave frequency in Hz; f0 is the resonant frequency in Hz; and ρ is the air density in kg / m³. 3 c is the speed of sound, in m / s; S is the cross-sectional area of ​​the channel, in m². 2 R is the acoustic resistance; α is the sound absorption coefficient; L is the silencer length in meters; P is the channel circumference in meters. These parameters are used to calculate the resonant silencing and resistive silencing.

[0109] In step 4, when the intake pressure drops beyond a preset safety threshold ΔP safe When the host protection system is triggered, the security threshold is met: Where, ΔP safe This is a preset safety threshold, in bar; P min Minimum allowable intake pressure, measured in bar, is the minimum intake pressure required to ensure normal engine operation. The nominal intake pressure, in bar, is the standard intake pressure under normal engine operating conditions, and ΔP safe Calculated dynamically using the following formula: Where L is the engine load, expressed as a percentage, and the formula dynamically adjusts the safety threshold based on the engine load.

[0110] In step 5, after the combustion efficiency is improved, the engine thermal efficiency η th satisfy: Where, η th To improve engine thermal efficiency after combustion efficiency; The original thermal efficiency; Δη meoh Improved thermal efficiency resulting from improved methanol combustion; Δη heat (The improvement in thermal efficiency brought about by waste heat recovery), and: (where Δη) meoh In the middle, m meoh Q is the methanol mass flow rate, expressed in kg / s. LHV,meoh The lower heating value of methanol is 19.9 MJ / kg; η comb,meoh The methanol combustion efficiency is 98%; P out Output power, in kW; Δη heat In this context, Qrec represents the recovered heat, measured in kW; η rankine For the Rankine cycle efficiency, the value is 12%. These formulas are used to calculate the increase in thermal efficiency due to methanol combustion and waste heat recovery.

[0111] In step 4, the optimal control curves for valve opening under different loads are obtained through genetic algorithm optimization, with the objective function being: Among them, F(C v Let C be the objective function value. The optimal valve opening C is determined by minimizing this value through optimization. v ;ΔR meoh The increase in methanol substitution rate, ΔR, is used to measure the extent to which methanol replaces diesel. meoh The maximum possible substitution rate is set to 12%. The weighting coefficient w1, which reflects the normalization of the methanol substitution rate increase in the objective function, is set to 0.45, indicating the degree of importance attached to increasing the methanol substitution rate; ΔP in P represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. max The maximum allowable intake pressure drop is set to 0.6 bar. To reflect the normalization considerations of the intake pressure reduction in the objective function, w2 is set to 0.25; ΔT exh This represents the increase in exhaust temperature, expressed in degrees Celsius (°C), reflecting the change in exhaust temperature after valve opening adjustment (T). max The maximum permissible exhaust temperature rise is set at 60°C. This represents the normalized weight of the exhaust temperature rise in the objective function, with w3 taking a value of 0.15; NO x The optimized nitrogen oxide emission value, The nitrogen oxide emission values ​​before optimization. The value of w4, representing the proportion of nitrogen oxide emission changes in the objective function, is 0.15, used to balance the importance of emission control in the optimization objective. By iteratively optimizing this objective function using a genetic algorithm, the optimal valve opening C for overall engine performance under different loads can be determined. v Control curve.

[0112] Experimental Data: In-depth Test Results of Applying this Method to a Medium-Speed ​​Diesel-Methanol Dual-Fuel Engine

[0113] I. Comparison Experiment of Methanol Injection Timing (25% Load)

[0114]

[0115] Data Explanation:

[0116] When the injection timing is adjusted to TDC0°, the overlap angle reaches 12°, the exhaust waste heat fully heats the methanol vapor, the vaporization temperature is increased by 40° compared with the bottom dead center injection, and the combustion efficiency is increased by 16%, which verifies the necessity of "injection timing and overlap angle optimization" in claim 1.

[0117] II. Comparative Experiment of Manual / Electric Valves (50% Load)

[0118] Valve type Opening control accuracy Temperature control fluctuation Substitution rate stability Response time Manual valve ±5％ ±5℃ ±1.5％ 810 seconds Electric valves ±1％ ±2℃ ±0.8％ 12 seconds

[0119] Data Explanation:

[0120] Although electric valves offer higher control precision (±1%), manual valves can still achieve a 40°C increase in exhaust temperature and a 7% increase in replacement rate at 50% load, consistent with the conclusion in claim 3 that "the valve type has a negligible impact on the effect," thus verifying the economic efficiency of the technical solution.

[0121] III. Adaptability Tests for Different Aircraft Models

[0122] Engine displacement Recommended valve specifications Optimal opening Exhaust temperature increase Increased substitution rate 15L DN40 22% (25% load) 28℃ 4.8％ 30L DN50 52% (50% load) 42℃ 7.2％ 50L DN80 68% (75% load) 48℃ 9.5％

[0123] Data Explanation:

[0124] Different displacement engines can achieve a 5% to 10% increase in replacement rate by adapting valve specifications (DN40 DN80), which verifies the adaptability of "selecting ball valve specifications according to intake volume" in claim 3, and is applicable to 10L and 50L medium-speed engines.

[0125] IV. Long-term operational reliability data (5000 hours of continuous operation)

[0126]

[0127] Data Explanation:

[0128] Due to improved combustion efficiency and reasonable control of exhaust temperature, the optimized engine reduces piston ring wear by 15% and exhaust valve carbon deposits by 30.8%, which is consistent with the inference in claim 9 that "improved combustion efficiency can extend equipment lifespan," and maintenance costs decrease by approximately 20%.

[0129] V. Mode Switching Performance Data

[0130] 1. Diesel → Dual-fuel switch (25% load)

[0131] Switching time: 8 seconds (originally 15 seconds)

[0132] Power fluctuation: ±3% (originally ±8%)

[0133] Methanol injection synchronization: delay <50ms

[0134] 2. Dual-fuel to diesel switching (75% load)

[0135] Purging time: 12 seconds

[0136] Residual methanol concentration: <0.5% (originally 2.3%)

[0137] Emissions exceeding the limit time: 0 seconds (originally 5 seconds).

[0138] Data Explanation:

[0139] The switching timing control (claim 6) makes mode switching smoother, reduces residual methanol concentration by 78%, and avoids excessive emissions during switching, making it suitable for scenarios such as ships that require frequent fuel switching.

[0140] VI. Safety Testing under Extreme Operating Conditions

[0141] 1. High-altitude environment (3000 meters above sea level)

[0142] Intake pressure compensation: Maintains an exhaust temperature rise of 35°C by automatically opening the valve by 15%.

[0143] The replacement rate increased by 4.5% (a decrease of 0.5% compared to the plain), verifying the environmental adaptability of the "dynamic safety threshold" in claim 8.

[0144] 2. High-temperature environment (40℃)

[0145] The intake and exhaust strategies automatically adjust the opening by +5% to prevent excessively high exhaust temperatures.

[0146] Thermal efficiency fluctuation: <1%, system operates stably.

[0147] The specific usage and function of this embodiment: In this invention, this patent focuses on a medium-speed diesel-methanol dual-fuel engine, aiming to improve methanol combustion efficiency. Its specific usage revolves around optimizing injection timing and intake / exhaust strategies, playing a key role in improving methanol substitution rate, reducing emissions, and enhancing system adaptability.

[0148] Methanol injection timing adjustment: Set the methanol injection timing to the intake top dead center (TDC) at 0°. At this position, the piston's downward movement allows as much methanol vapor as possible to enter the cylinder without overflowing into the exhaust pipe. Simultaneously, this position represents the maximum overlap angle between methanol entering the cylinder and the exhaust valve closing; the exhaust valve is not yet closed, and the residual heat from the exhaust gas in the cylinder can directly heat the incoming methanol vapor, creating conditions for complete methanol vaporization. In actual operation, precise control of the injection system is required to ensure methanol is injected at this specific moment, with crankshaft angle accuracy controlled within ±0.5° to guarantee the stability of the technical performance.

[0149] Intake and Bleed-Out Device Operation: Install a bleed-out device, such as a manual or automatic ball valve, in the intake chamber of the main engine (select the appropriate specification based on the main engine's intake volume, such as a DN50 ball valve). When the main engine is running in diesel mode, close the bleed-out valve to ensure sufficient oxygen for complete combustion of the diesel fuel injected into the cylinder. When the main engine switches to methanol dual-fuel mode, adjust the opening of the bleed-out valve according to the intake pressure and exhaust temperature under different loads. At 25% load, manually adjust the valve opening to approximately 20%. At this time, the main engine's detection and alarm system shows an intake pressure drop of approximately 0.3 bar and an exhaust temperature rise of 30°C. At 50% load, the valve opening is approximately 50%, the intake pressure drops by approximately 0.3 bar, and the exhaust temperature rises by 40°C. During operation, the main engine's detection and alarm system collects sensor data and displays the intake pressure and exhaust temperature in real time. Based on this, the valve opening is precisely controlled to optimize the engine's operating status.

[0150] Improving methanol combustion efficiency and substitution rate: By adjusting the methanol injection timing to the top dead center (TDC) of the intake air, utilizing exhaust waste heat to heat methanol vapor, and combining this with intake venting to increase exhaust temperature, the heat required for methanol vaporization (the latent heat of methanol vaporization is 1109 kJ / kg) can be fully compensated, allowing for better methanol vaporization and combustion, thereby improving methanol combustion efficiency. Under different loads, the methanol substitution rate is significantly improved; for example, it increases by 5% at 25% load and by 10% at 75% load. This not only reduces dependence on diesel fuel but also reduces fuel costs. Taking a 2000kW main engine as an example, operating for 300 days a year can save 120 tons of diesel fuel, reducing costs by 840,000 yuan.

[0151] Reduced emissions: By employing an intake and exhaust system, nitrogen oxide (NOx) generation in methanol mode can be reduced. Experimental data shows that, at 50% load, a certain 6-cylinder engine reduced NOx emissions from 4.2 g / kWh to 3.1 g / kWh, and particulate matter (PM) emissions decreased by approximately 10% simultaneously. This allows the engine emissions to meet stringent environmental requirements such as the International Maritime Organization (IMO) Tier III emission standards, thus reducing environmental pollution.

[0152] Enhanced System Adaptability and Stability: This patented technology is applicable to both manifold injection and direct injection systems in medium-speed diesel-methanol dual-fuel engines, effectively improving methanol combustion efficiency across a load range of 25% to 100%. Precise control of valve opening under varying loads ensures stable engine operation under diverse conditions. When the load changes abruptly, such as from 50% to 75%, the system responds quickly, adjusting the valve opening within 1.5 seconds, with speed fluctuations less than ±1.5%, guaranteeing engine stability and reliability.

Claims

1. A method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine, characterized in that, Includes the following steps: Step 1: Methanol Injection Timing Optimization: Adjust the methanol injection timing to the intake top dead center (TDC) at 0°. This injection timing ensures that the crankshaft angle accuracy is controlled within ±0.5°, and the overlap angle α formed by the methanol injection start point and the exhaust valve closing point satisfies the formula: α=θ inj -θ evc Where α is the overlap angle, measured in °CA (crankshaft angle), used to measure the degree of time overlap between methanol injection and exhaust valve closure; θ inj θ represents the methanol injection initiation angle, in °CABTDC, and the crankshaft rotation angle before top dead center, indicating the angle of the crankshaft relative to top dead center when methanol injection begins; evc The exhaust valve closing angle is expressed in °CABTDC, which is the angle of the crankshaft relative to the top dead center when the exhaust valve is closed. α must be within the range of 5° to 15° to ensure good heat exchange conditions. Step 2: Intake System Modification: Install a venting device in the main unit's intake chamber. The venting device includes an electric actuator, a flow regulating valve, and a pressure sensor. The valve's flow capacity is C. v Satisfying the formula: Among them, C v The flow capacity of a valve is an important parameter for measuring its flow characteristics; Q represents the gas flow rate, measured in cubic meters per second (m³). 3 / h refers to the gas volume flow rate through the valve; ΔP is the pressure difference across the valve, in bar, reflecting the pressure change across the valve; ρ 20 The density of air at 20℃ is expressed in kg / m³. 3 ρ is the standard reference density; ρ is the actual gas density under operating conditions, in kg / m³. 3 It varies due to factors such as temperature and pressure during actual operation; Step 3: Dual-mode control strategy: When the main unit is running in diesel mode, the venting device valve is closed. At this time, the oxygen concentration (O2%) in the intake chamber satisfies the formula: Wherein, O2% is the percentage of oxygen concentration in the intake chamber; V air The volume of air entering the intake chamber, expressed in m³. 3 ; 0.21 is the volume percentage of oxygen in the air; V res The volume of residual gas in the intake chamber, in cubic meters (m³). 3 This formula is used to calculate the oxygen concentration in the intake chamber, which needs to be maintained within the range of 20.5% to 21% to ensure complete combustion of diesel fuel. Step 4: Load Adaptive Adjustment: Based on the intake pressure Pin (bar) and exhaust temperature Texh (°C) of the main unit under different loads L (%), the opening amplitude Cv of the vent valve is controlled by PID control. The control algorithm satisfies: Among them, C v (t) represents the opening degree of the venting valve at time t; K p K is the proportional coefficient used to quickly address the deviation. i K is the integral coefficient, used to eliminate steady-state error; d is the differential coefficient, which predicts the trend of deviation change; e(t) is the deviation between the setpoint SP and the actual load L(t); The integral term of the error. K is the differential term of the error; at 25% load, K p =0.8, K i =0.02, K d =0.1, these parameters determine the adjustment effect of valve opening; Step 5: Improve combustion efficiency: By adjusting the timing of methanol injection and the combined effect of intake and exhaust, the compensation amount Q of the latent heat of methanol vaporization is increased. comp Satisfying the formula: Q comp =m meoh ·ΔH v ·η heat ; where Q comp This is the compensation amount for the latent heat of methanol vaporization, expressed in kJ, used to measure the heat required to supplement methanol vaporization; m meoh The mass of methanol is expressed in kg; ΔH v The latent heat of methanol vaporization, with a value of 1109 kJ / kg, represents the heat absorbed during the methanol vaporization process; η heat Heat exchange efficiency (reflecting the effectiveness of heat transfer), and η heat Calculated using the exhaust waste heat recovery coefficient φ and the intake air temperature rise coefficient γ: in, To optimize the intake air temperature, the unit is K; To optimize the front airflow temperature, the unit is K; c p Specific heat capacity of air, unit: kJ / kg·K; m air Q is the air mass flow rate, expressed in kg / s. exh φ represents the exhaust heat, expressed in kJ / s; φ is the exhaust waste heat recovery coefficient, ranging from 0.35 to 0.45, used to measure the degree of exhaust waste heat recovery and utilization.

2. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 2, the valve opening C of the venting device v With engine load L and intake pressure P in Exhaust temperature T exh The relationship satisfies the three-dimensional mapping function: C v =f(L,P in ,T exh )=a0+a1L+a2P in +a3T exh +a4LP in +a5LT exh +a6P in T exh +a7LP in T exh , where C v P represents the vent valve opening; L represents the engine load, expressed as a percentage; P represents the vent valve opening. in T represents intake pressure, measured in bar. exh The exhaust temperature is expressed in °C; a0, a1, a2, a3, a4, a5, a6, and a7 are function coefficients, with values ​​of 12.5, 0.85, 15.2, 0.12, 0.03, 0.0015, 0.002, and 0.00005, respectively.

3. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 4, the valve opening C under different loads v The following relationship exists between the intake pressure drop ΔPin and the exhaust temperature rise ΔTexh: 25% load: 50% load: 75% load: 100% load: Among them, C v Valve opening, expressed as a percentage; ΔP in ΔT represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. exh This represents the increase in exhaust temperature, expressed in °C, reflecting the change in exhaust temperature after adjusting the valve opening.

4. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 5, the increase in methanol substitution rate Rmeoh and the increase in exhaust temperature ΔTexh satisfy an exponential relationship: Where, ΔR meoh R0 represents the increase in methanol substitution rate, used to measure the degree of increase in the proportion of diesel replaced by methanol; R0 is the maximum substitution rate increase potential, with a value of 12%; λ is the temperature sensitivity coefficient, with a value of 0.025℃⁻¹, reflecting the degree of influence of exhaust temperature changes on the increase in methanol substitution rate; ΔT exh This represents the exhaust temperature rise, in °C, and this relationship exists over ΔT. exh When the temperature is between 20℃ and 60℃, the error shall not exceed ±1.2%.

5. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 4, the adaptive adjustment of the PID control parameters satisfies the Ziegler-Nichols method: proportionality coefficient K p : Integral coefficient K i : Differential coefficient K d : Among them, K p K i K d These are the proportional, integral, and derivative coefficients for PID control; K u The critical gain is the proportional gain of the system when it is in a critical steady state; T u The critical oscillation period is the oscillation period of the system in the critical steady state; L is the engine load, expressed as a percentage. These formulas are used to adaptively adjust the PID control parameters according to the engine load.

6. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, The switching process between diesel mode and methanol dual-fuel mode in step 3 satisfies the following timing control: Diesel → Dual-fuel switch: Among them, t trans t0 is the switching time from diesel mode to dual-fuel mode, in seconds; t0 is the start-up time, in seconds; V pipe This refers to the intake manifold volume, measured in cubic meters (m³). 3 Q air Airflow rate, unit: m³ / s 3 / s; τ is a time constant with a value of 5s. This formula is used to calculate the time required for mode switching. Dual-fuel to diesel switching: Among them, t purge The purging time for switching from dual-fuel mode to diesel mode, in seconds; V cyl Total cylinder volume, in cubic meters (m³). 3 n is the engine speed, in rpm; Δt is the time of a single cycle, in seconds; V stroke The stroke volume is expressed in cubic meters (m³). 3 This formula is used to determine the purging time when switching modes to remove residual methanol gas.

7. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, The silencing device of the venting device in step 2 adopts an impedance composite structure, and its noise reduction NR satisfies: NR = NR res +NR abs ; Wherein, NR represents the total noise reduction of the silencing device, measured in dB; NR res This refers to resonant noise reduction, measured in dB, which eliminates noise at specific frequencies through the principle of resonance; NR abs The resistive noise reduction is expressed in dB (using sound-absorbing materials to absorb noise energy), and: Where f is the sound wave frequency in Hz; f0 is the resonant frequency in Hz; and ρ is the air density in kg / m³. 3 c is the speed of sound, in m / s; S is the cross-sectional area of ​​the channel, in m². 2 R is the acoustic resistance; α is the sound absorption coefficient; L is the silencer length in meters; P is the channel circumference in meters. These parameters are used to calculate the resonant silencing and resistive silencing.

8. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 4, when the intake pressure drops beyond the preset safety threshold ΔP safe When the host protection system is triggered, the security threshold is met: Wherein, ΔP safe This is a preset safety threshold, in bar; P min Minimum allowable intake pressure, measured in bar, is the minimum intake pressure required to ensure normal engine operation. The nominal intake pressure, in bar, is the standard intake pressure under normal engine operating conditions, and ΔP safe Calculated dynamically using the following formula: Where L is the engine load, expressed as a percentage, and the formula dynamically adjusts the safety threshold based on the engine load.

9. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, After the combustion efficiency is improved in step 5, the engine thermal efficiency η th satisfy: Where, η th To improve engine thermal efficiency after combustion efficiency; The original thermal efficiency; Δη meoh Improved thermal efficiency resulting from improved methanol combustion; Δη heat (The improvement in thermal efficiency brought about by waste heat recovery), and: Where, Δη meoh In the middle, m meoh Q is the methanol mass flow rate, expressed in kg / s. LHV,meoh The lower heating value of methanol is 19.9 MJ / kg; η comb,meoh The methanol combustion efficiency is 98%; P out Output power, in kW; Δη heat In this context, Qrec represents the recovered heat, measured in kW; η rankine The efficiency of the Rankine cycle is 12%.

10. The method for improving methanol combustion efficiency in a medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that, In step 4, the optimal control curves for valve opening under different loads are obtained through genetic algorithm optimization, with the objective function being: Among them, F(C v Let C be the objective function value. The optimal valve opening C is determined by minimizing this value through optimization. v ;ΔR meoh The increase in methanol substitution rate, ΔR, is used to measure the extent to which methanol replaces diesel. meoh The maximum possible substitution rate is set to 12%. The weighting coefficient w1, which reflects the normalization of the methanol substitution rate increase in the objective function, is set to 0.45, indicating the degree of importance attached to increasing the methanol substitution rate; ΔP in P represents the decrease in intake pressure, expressed in bar, reflecting the effect of valve opening changes on intake pressure. max The maximum allowable intake pressure drop is set to 0.6 bar. To reflect the normalization considerations of the intake pressure reduction in the objective function, w2 is set to 0.25; ΔT exh This represents the increase in exhaust temperature, expressed in degrees Celsius (°C), reflecting the change in exhaust temperature after valve opening adjustment (T). max The maximum permissible exhaust temperature rise is set at 60°C. This represents the normalized weight of the exhaust temperature rise in the objective function, with w3 taking a value of 0.15; NO x The optimized nitrogen oxide emission value, The nitrogen oxide emission values ​​before optimization. The value of w4, representing the proportion of nitrogen oxide emission changes in the objective function, is 0.15, used to balance the importance of emission control in the optimization objective. By iteratively optimizing this objective function using a genetic algorithm, the optimal valve opening C for overall engine performance under different loads can be determined. v Control curve.

Images