Investigation on Pre-ignition and Super-Knock in Highly Boosted Gasoline Direct Injection Engines 2014-01-1212
High boost and direct injection hold the potential of enhanced power density and fuel consumption in the development of gasoline engines. However, super-knock with strong destructiveness was widely reported at low-speed and high-load operating regime in turbocharged GDI engines. The objective of this study is to clarify the characteristics of super-knock and to try to find some feasible solutions to suppress super-knock.
To fast evaluate super-knock at low-speed and high-load regime, a rapid test procedure including three super-knock test sections of 5000 cycles with 3 idle operations, was proposed. The experimental data indicate that pre-ignition is not the sufficient condition for super-knock. Pre-ignition may lead to super-knock, heavy knock, slight knock, and non-knock. Compared with conventional knock, knock intensity of super-knock is much higher and the maximum amplitude of pressure rise at start of knock is more than one order of magnitude higher.
This paper also clarifies that the injection strategies highly influence the frequency of super-knock occurrence in the turbocharged GDI engine. Double injection during intake stroke (DII) is an efficient way to suppress super-knock in test engine. The simulated results indicate that DII can shorten spray penetration, suppress fuel droplet attached on piston top and cylinder liner.