The first wide-open throttle engine cycle: Transition into knock experiments with fast in-cylinder sampling

Abstract

A gasoline cooperative fuels research (CFR) engine is used to evaluate the knock sensitivity for the first wide-open throttle (WOT) cycle during fast throttle transitions at various fuelling levels. A fast flame ionization detector (FFID) and fast non-dispersive infrared (NDIR) detector are used to determine an accurate in-cylinder air—fuel ratio. All tests are done with compression ratio = 9 and spark timing set to 20° BTC, conditions that normally result in moderate knock during steady state operation. It is found that audible knock occurs in 60–80 per cent of cases when in-cylinder P is between 1.05 and 1.35. However, if the first WOT cycle fuelling results in an in-cylinder air—fuel ratio slightly less than stoichiometric, knock remains inaudible. This slightly lean of stoichiometric fuelling also provides for the strongest gross indicated mean effective pressure due to appropriate combustion phasing without knock.