Methods to Reduce End Gas Temperatures for Lower Knocking Sensitivity - A Simulation Study Stop Start for Future Boosted Gasoline Engines

摘要

Irregular combustion events such as knocking and, more severe, pre=ignition are the major hurdles to achieving a better efficiency of gasoline engines at high load. The common counter measure is to delay spark timing, which results into a lower thermal efficiency of the high-pressure cycle. Thus, to achieve the target torque curve the engine has to be boosted harder, resulting into higher air and fuel consumption. Under the influence of knock, less fuel energy is converted into piston work; and due to lower peak firing pressure also heat transfer to the coolant water to some extent is reduced in comparison to ideal combustion timing. Hence more fuel energy leaves the engine cylinder as higher exhaust gas temperature. Where later spark timing does not solve the problem, or spark timing has to be delayed to a point where combustion stability is no longer acceptable, additional fuel is injected to lower the mixture temperature by its latent heat.