Investigations on Mixture Formation during Start-UP Process of a Two-Stage Direct Injection Gasoline Engine for HEV Application 2013-01-2657

A cycle-resolved test system was designed in a Two Stage Direct Injection (TSDI) Gasoline engine to simulate the engine quick start process in an Integrated Start and Generator (ISG) Hybrid Electric Vehicle (HEV) system.

Based on the test system, measurement of the in cylinder HC concentrations near the spark plug under different engine coolant temperature and cranking speed conditions were conducted using a Fast Response Flame Ionization Detector (FFID) with Sampling Spark Plug (SSP) fits, then the in-cylinder equivalence ratio near the spark plug was estimated from the measured HC concentrations. In addition, the effects of the 1^st injection timing, 2^nd injection timing, and total equivalence ratio on the mixture formation near the spark plug were analyzed by means of experiments.

Results showed that coolant temperature, cranking speed, fuel injection timing especially the 2^nd injection timing and total equivalence ratio play a substantial part in the mixture formation of the TSDI engine. Compared with that under the condition of 10°C, peak HC concentrations increased by 30% at the coolant temperature of 85°C and equivalence ratio near the spark plug at TDC get s an increase. HC concentrations near the spark plug at TDC is decreased by 51.7% and equivalence ratio near the spark plug at TDC has got a reduction at the cranking speed of 1400r/min, compared with that at 400r/min. HC concentrations increased with the advance of the 1^st and the 2^nd injection timing BTDC. Peak HC concentrations increase obviously and equivalence ratio near the spark plug at TDC increases when the 1^st injection timing advanced from 190°CA BTDC to 290°CA BTDC and the 2^nd injection timing advanced from 20°CA BTDC to 80°CA BTDC. When the total equivalence ratio increases from 0.85 to 1.19, equivalence ratio near the spark plug at TDC gets an increase.

Based on these measurements the optimal parameter setting for every subsequent ignition during the engine start-up can be derived.