Experimental Research On Knocking Of Combining High Compression Ratio With Dual-Independent Cam Timing For A Boosted Direct-Injection Engine

Nowadays, with the rise in oil prices and increasing concern of environmental problem energy-saving and emission-reduction has became an important policy for many countries. The oil consumed by the vehicle accounts for a great proportion in the oil consumption of the world. So how to improve the fuel economy of the gasoline engine becomes a hot research topic. Pumping loss is an unfavorable factor to reduce the fuel consumption for gasoline engine. To improve the fuel economy of gasoline engine by reduce pumping loss, downsizing is becoming an important trend for automobile industry. To meet the consumer's requirement for power, turbocharger is usually used in a downsizing engine. So more and more companies focus on the boost and direct-inject technologies for their downsizing engine. Because the downsizing boosted direct-injection engine has very high Thermal-load, the knocking intensity and exhaust temperature are higher than traditional gasoline engine. To suppress knocking, the spark timing has to be retarded. On full load of high speed, knock presents less of a problem but any spark retard at this power levels results in excessive exhaust temperature, which require enrichment. But retard the spark timing and enrichment will have negative effect on the fuel economy , so knock become an barrier to further downsizing. Knock has become a hot research area in the world. In this paper, we do the experimental research on a dual-VVT turbocharged direct-injection gasoline engine. The purpose is to find how the control parameters affect the knocking and other performance of the engine. Besides we investigated how to reduce knocking of the engine with high compression ratio by late intake-valve–closing (LIVC) strategy or cooled external EGR technology.The result shows that knocking can be suppressed by retard the Intake valve opening (IVO) or Exhaust valve closing (EVC). The fuel economy can be greatly improved by decrease the overlap on the high load or increase the overlap on the part load. The start of injection (SOI) and fuel injection pressure (FP) mainly affect the soot emission. The knocking can be suppressed by retard the SOI a little. The FP nearly has no influence on knocking. If the mixture be enriched, knocking can be suppressed and the NOX emission reduce but the fuel consumption get worse. Knocking can also be suppressed by decrease the intake temperature. Besides the EGR technology and LIVC strategy can suppress knock, so the engine can use higher compression ratio when use EGR technology or LIVC strategy.