Development of fast idle catalyst light-off strategy for gasoline compression ignition engine – Part 2 2020-01-0314
The present investigation expands on our previous work on development of fast idle catalyst light-off strategy for a light duty gasoline compression ignition (GCI) engine in spark ignition mode. The steady state experimental investigation in a single cylinder GCI engine indicates tailed injection strategy: 1) start of first injection (SOI1st) = -350 CAD aTDC 2) start of second injection (SOI2nd) = 15 CAD aTDC and 3) spark timing = 15 CAD aTDC as optimum for effective catalyst light off in a shorter time. A sensitivity study was performed to investigate the impact of lambda, load, speed, spark plug design and injector spray pattern on effective cold start catalyst light off at the reported optimum fuel injection strategy. The results indicate that higher load is useful to obtain better combustion stability and higher exhaust temperature at expense of increased fuel consumption and emission. At higher speeds, increased exhaust temperature is attained but with NOX and COV penalty. Lean operation (Lambda = 1.05) has a better compromise in terms of COV and emissions. Dynamic operation at the optimum tailed injection strategy resulted in few initial misfired cycles due to poor combustion stability (for less than 10 secs after). Therefore, the spark timing is advanced during the first part of fast idle catalyst warm up period to reduce the misfiring and minimize hydrocarbon and CO breakthrough. Based on the dynamic testing results, we split the initially proposed control strategy in two parts – firstly, transient combustion control strategy during first part of fast idle phase (less than 10 secs) for rapid engine warm up and effective catalyst light off (light off phase 1) secondly, split fuel injection and extremely retarded spark timing strategy is proposed during the second part of catalyst warm up period to generate high enthalpy flow in the exhaust with reduced hydrocarbon and other emissions, improved combustion stability, and fuel economy (light off phase 2). In summary, the dynamic experimental results from this study would provide base data to validate feasibility and/or in support of after treatment system development.