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Abstract
The lean-burn capability of the Diesel-ignited gas engine combined with its potential for high efficiency and low CO 2 emissions makes this engine concept one of the most promising alternative fuel converters for passenger cars. Instead of using a spark plug, the ignition relies on the compression-ignited Diesel fuel providing ignition centers for the homogeneous air-gas mixture. In this study the amount of Diesel is reduced to the minimum amount required for the desired ignition. The low-load operation of such an engine is known to be challenging, as hydrocarbon (HC) emissions rise. The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate. A physical engine model helps to investigate three important limitations, namely maximum acceptable HC emissions, minimal CO 2 reduction, and minimal exhaust gas temperature. An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation. The simulations on the various low-load strategies reveal the conflicting demand of lean combustion with low CO 2 emissions and stoichiometric operation with low HC emissions, as well as the minimal feasible dual-fuel load of 3.2 bar brake mean effective pressure.
Highlights
The objective of this study is to develop optimal low-load operation strategies for the input variables equivalence ratio and exhaust gas recirculation (EGR) rate
An important finding is the fact that the high HC emissions under low-load and lean conditions are a consequence of the inability to raise the gas equivalence ratio resulting in a poor flame propagation
This study focuses explicitly on the low-load limitations implied by HC emissions, CO2 emissions, and exhaust gas temperature while attention was paid to the extensibility of the model presented such that a nitrogen oxide emissions (NOx) submodel can be integrated seamlessly at a later time
Summary
The importance of natural gas as a hydrocarbon-based fuel for engines in industrial, naval and automotive applications is increasing continually. The potential low CO2 emission of methane, favored on the one hand by the high hydrogen-to-carbon ratio and on the other hand by the high knock resistance, makes natural gas one of the most promising alternative energy carriers for passenger cars. Methane, obtained from fossil sources as well as from synthetic production, will likely be available in substantial quantities in the future. The production of methane by excess electric energy based on electrolysis may help to mitigate the problem of balancing demand and supply in the power network with renewable energy sources. Engines fueled with this synthetic methane operate CO2 -neutrally
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