Diesel Engine Internal EGR Valve Timing for Low Cetane Ignition
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Solution Overview
Problem
Diesel engines with low compression ratios face challenges in maintaining self-ignition conditions, especially at low load and low rotation speeds, due to decreased cylinder temperatures and degraded ignition performance with fuels of lower cetane numbers.
Innovation Solution
The diesel engine introduces internal EGR gas during the intake stroke by opening the exhaust valves, with specific lift properties and timing to increase cylinder temperatures and ensure self-ignition, using a geometric compression ratio between 12:1 to 15:1, and adjusting the exhaust valve opening area ratio relative to the intake valve area to satisfy self-ignition conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the geometric compression ratio is set low (12:1 to 15:1) to reduce NOx emissions and improve thermal efficiency, then NOx discharge amount is reduced and thermal efficiency is improved, but the cylinder temperature at the end of compression stroke decreases making self-ignition difficult to achieve
Solution Approach 1:
The exhaust valve is opened during the intake stroke to introduce hot exhaust gas (internal EGR) into the cylinder before compression begins. This preliminary heating action ensures that even with the lower compression ratio, the cylinder temperature at the end of compression reaches the threshold needed for self-ignition of diesel fuel.
Solution Approach 2:
The invention changes the temporal parameter of valve operation by opening the exhaust valve during the intake stroke rather than only during the exhaust stroke. This timing change allows hot exhaust gas to be introduced into the cylinder, raising the initial temperature for compression and enabling self-ignition at lower compression ratios.
2Loss of energy
If the geometric compression ratio is set low to improve thermal efficiency, then thermal efficiency is improved, but the combustion rate subsides making self-ignition difficult under low load and low rotation speed conditions
Solution Approach 1:
Hot exhaust gas is introduced into the cylinder during the intake stroke to preheat the charge air. This preliminary heating action compensates for the reduced compression heating effect at low compression ratios, ensuring reliable self-ignition conditions are achieved even during low load and low rotation speed operation.
Solution Approach 2:
The exhaust gas acts as an intermediary medium that transfers thermal energy from the exhaust system to the intake charge. This thermal intermediary enables the low compression ratio engine to achieve sufficient ignition temperature without requiring higher compression ratios that would improve thermal efficiency further.
3Temperature
If the exhaust valve is opened during the intake stroke to increase cylinder temperature, then self-ignition conditions are satisfied, but the intake passage becomes choked
Solution Approach 1:
The exhaust valve is opened only partially during the intake stroke rather than being fully open throughout. The opening area is precisely controlled to provide sufficient hot exhaust gas for ignition temperature while limiting the degree of intake passage choking to maintain adequate air flow for combustion.
Solution Approach 2:
The invention changes the parameter of valve opening area by defining a specific ratio relationship between exhaust valve opening area and intake valve opening area. This parameter control balances the competing requirements of raising cylinder temperature through exhaust gas introduction while maintaining sufficient intake air flow.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration secures fuel ignitability and reduces NOx emissions while improving thermal efficiency and exhaust emission performance by ensuring self-ignition even with low cetane number fuels, enhancing engine performance across varying operating conditions.
Implementation Method 1
internal EGR gas is introduced into cylinders by opening (re-opening) exhaust valves during an intake stroke
Implementation Method 2
a temperature of the engine at the end of a compression stroke is decreased corresponding to the low compression ratio
Data Source
AI summary
A diesel engine body is provided with a geometric compression ratio ε within a range of 12:1 to 15:1. The engine body has an intake valve for opening and closing an intake passage of a cylinder, an exhaust valve for opening and closing an exhaust passage of the cylinder, and an exhaust gas re-circulation passage communicating with the intake and exhaust passages and for partially re-circulating exhaust to the intake passage. During low engine load and rotation speed conditions, the exhaust valve is opened during an intake stroke, and the intake passage is choked. The exhaust valve is closed before the intake valve in the later stage of the intake stroke. An opening area SE of the exhaust valve is set so that a ratio of SE to an opening area SI of the intake valve meets a relation of:0.01×(15−ε)+0.02≦SE/SI≦0.17.