Combustion Stability Improvement via Multiple Ignition Sites on a 4-cylinder Production Engine 2020-01-1115
For SI engines, further improvement of engine efficiency has become the major development trend, and lean burn/EGR technologies as well as intensified in-cylinder flow need to be adapted to reach that target. Stronger ignition sources become more favorable under extreme lean/EGR conditions. Among the ignition technologies developed, multiple ignition sites technology has been proved to be an effective way to help with the initial flame kernel development. In this paper, a spark ignited 4-cylinder turbo-charged production engine is employed to investigate the impact of multiple ignition sites technology on engine performance under EGR condition. Four in-house designed 3-core sparkplugs are installed on the cylinder to generate multiple ignition sites in the cylinders. The engine is equipped with a variable valve train (VVT) system, so internal EGR can be introduced through cam timing adjustment. Under partial load, the pumping loss can be effectively reduced when internal EGR rate is increased, so the engine efficiency can be improved. However, combustion stability becomes worse in terms of higher cycle to cycle variation of the engine IMEP. Compared with traditional sparkplugs, the multiple ignition sites technology can tolerate higher internal EGR rate with shorter ignition delay, which can effectively reduce the cycle to cycle variation and improve engine fuel economy.