Abstract
This study tried to improve ignitability of a lean-combustion CNG engine. CNG was directly injected into the combustion chamber by a gas injector and the gas-jet was ignited by a spark plug. The combination of gas-jet combustion and two-stage injection; namely, first injection at early combustion stroke and second injection just before ignition, has a great effect to realize lean-combustion at equivalence ratio ranges from 0.3 to 0.9 with high thermal efficiency and less CO emission. It is important for two-stage injection and gas-jet combustion system to control over-lean mixture distribution caused by the first injection for reduction of THC emission, and also to avoid excess-rich mixture formation near spark plug that results in incomplete combustion.
