Development of fast idle catalyst light-off strategy for Gasoline Compression Ignition engine – Part 1 2020-01-0316
The present investigation pertains to the development of fast idle catalyst light-off strategy for a light duty gasoline compression ignition (GCI) engine. The engine cold start fast idle operation poses a problem of increased criteria emissions if the catalyst is not activated during the warm up period. Therefore, a control strategy is proposed here to minimize the criteria pollutants during the fast idle phase via enabling fast catalyst light off in a GCI engine and relying on the spark ignition of a globally stoichiometric fuel air mixture. The engine has unique design features such as certain geometry configuration between spark plug and fuel injector arrangement, and the location of spark plug in a high compression ratio (CR) diesel-like combustion chamber. The experiments were performed in a single cylinder GCI engine at cold start fast idle conditions using certification gasoline fuel (RON 91). Split fuel injection and extremely retarded spark timing strategy are applied to generate high enthalpy flow in the exhaust pipe with reduced hydrocarbon and other emissions, improved combustion stability, and fuel economy. Based on the experimentation, split injection cases with two different second start of injection (SOI) via, 1) tailed injection case - SOI1st = -350 CAD aTDC and SOI2nd = 15 CAD aTDC, 2) intake injection case - SOI1st = -350 CAD aTDC and SOI2nd = -270 CAD aTDC, showed better results in terms of COV and criteria emissions when compared to other fuel injection cases. The steady state experimental results also indicate that, regardless of fuel injection strategy, retarded spark timing of 15 CAD aTDC is required to attain a higher exhaust temperature of around 700ºC to 800 ºC. Computational fluid dynamics (CFD) engine simulations confirmed that the fuel-air mixing induced by a fuel injection and in-cylinder flow motions determines the fuel-air mixture distribution around a spark plug and plays a crucial role in combustion instability. In summary, evaluation of cold start performance index identifies tailed injection strategy as optimum to generate higher exhaust energy without compromising the combustion stability to effectively light off the catalyst and reduce the criteria emissions.