Gaseous Engine SCR Control via Pilot Fuel Injection Timing
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Solution Overview
Problem
Gaseous-fuelled internal combustion engines face challenges in maintaining high NOx conversion rates in selective catalytic reduction (SCR) converters, especially when idling, due to lower exhaust gas temperatures, which are not effectively addressed by methods used in diesel-fuelled engines.
Innovation Solution
A control method that detects engine idling parameters to timing the injection of gaseous fuel and a pilot fuel to maintain exhaust gas temperatures above 200 degrees Celsius, ensuring efficient NOx conversion in the SCR converter by adjusting fuel injection timings and delaying gaseous fuel injection to increase exhaust gas temperature while limiting unburned fuel concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If gaseous fuel is injected into a conventional compression ignition engine, then cleaner burning is achieved, but reliable auto-ignition cannot be obtained under the same temperature and pressure conditions
Solution Approach 1:
A pilot fuel injector introduces a small quantity of diesel fuel as an intermediary substance that reliably auto-ignites under compression, triggering the ignition of the main gaseous fuel charge. This mediator enables the gaseous fuel to burn reliably without requiring modifications to the compression ignition system.
Solution Approach 2:
The fuel injection process is segmented into two separate injections: a first injection of pilot fuel (diesel) and a second injection of gaseous fuel. This segmentation allows each fuel type to be optimized for its specific combustion characteristics while working together to achieve reliable ignition and clean burning.
2Object-generated harmful factors
If SCR converter is applied to reduce NOx emissions, then significant NOx reduction is achieved, but the converter requires exhaust gas temperatures above a predetermined threshold to maintain high conversion rates
Solution Approach 1:
The injection timing of the gaseous fuel is adjusted as a controllable parameter to optimize exhaust gas temperature. By controlling when the gaseous fuel is injected and burned, the system maintains exhaust temperatures within the optimal range for SCR converter operation, ensuring high NOx conversion rates.
Solution Approach 2:
The system monitors exhaust gas temperature and adjusts fuel injection timing accordingly to maintain temperatures suitable for SCR converter operation. This feedback control ensures that the exhaust gas temperature remains above the predetermined threshold required for effective NOx reduction.
3Temperature
If gaseous fuel injection timing is delayed to increase exhaust gas temperature for SCR operation, then SCR converter efficiency is improved, but unburned fuel concentration in exhaust increases
Solution Approach 1:
The pilot fuel is injected and ignited before the main gaseous fuel injection. This preliminary action creates a hot combustion environment that ensures complete combustion of the subsequently injected gaseous fuel, preventing excessive unburned fuel in the exhaust while still achieving the temperature needed for SCR operation.
Solution Approach 2:
The system optimizes the gaseous fuel injection timing parameter to find the optimal balance point where exhaust temperature is sufficient for SCR operation but injection duration is limited to prevent excessive unburned fuel. This parameter optimization simultaneously addresses both requirements.
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
The method effectively maintains the SCR catalyst bed temperature above 200 degrees Celsius, enhancing NOx conversion efficiency and reducing tailpipe emissions in gaseous-fuelled engines, even during idling conditions.
Implementation Method 1
The ability of ammonia as a reductant to achieve a significant reduction of NOx has been proven for stationary power applications and therefore has been used in diesel-fuelled engines. Other forms of ammonia can be used, such as urea, aqueous, gaseous or liquid ammonia. Using an SCR converter, the SCR catalyst facilitates the reaction between ammonia and NOx to produce water and nitrogen gas.
Data Source
AI summary
A method controls a direct-injection gaseous-fuelled internal combustion engine system to improve the conversion efficiency of an SCR converter that is operative to reduce levels of NOx. The method comprises detecting when the internal combustion engine is idling and timing the injection of a first quantity of fuel to begin injection when the engine's piston is near top dead center; and controlling the temperature of exhaust gas to be above a predetermined temperature that is defined by an operating temperature range that achieves a desired conversion efficiency for the selective catalytic reduction converter, by: (a) timing injection of the gaseous fuel to begin after timing for injection the first quantity of fuel, and (b) increasing exhaust gas temperature by increasing a delay in timing for injecting the gaseous fuel, while limiting the delay to keep concentration of unburned fuel exiting the combustion chamber below a predetermined concentration.