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This paper presents large eddy simulation (LES) and experimental studies of the combustion process of ethanol/air mixture in an experimental optical HCCI engine. The fuel is injected to the intake port manifolds to generate uniform fuel/air mixture in the cylinder. Two different piston shapes, one with a flat disc and one with a square bowl, were employed to generate different in-cylinder turbulence and temperature field prior to auto-ignition. The aim of this study was to scrutinize the effect of in-cylinder turbulence on the temperature field and on the combustion process. The fuel tracer, acetone, is measured using laser induced fluorescence (LIF) to characterize the reaction fronts, and chemiluminescence images were recorded using a high speed camera, with a 0.25 crank angle degree resolution, to further illustrate the combustion process. Pressure in the cylinder is recorded in the experiments.

Several studies have shown that NO has a strong influence on engine knock. This paper reports an experimental study that addresses the connection between SI engine knock and the level of nitric oxide, NO, in the intake manifold gas under various conditions of engine operation. Some theories explain the second ion-current peak as thermal ionisation of NO. Both temperature and NO concentration is of importance. By advancing the ignition angle the NO concentration can be increased, but the temperature is also increased. Addition of NO in the inlet manifold increases the NO concentration but has less effect on the temperature. SI engine experiments were conducted over a number of different ignition timings, air/fuel ratios, engine speeds and intake manifold pressures. The NO level in the intake manifold was altered from 100 to 1600 ppm, increasing the amount by doubling. The study confirms that there is an increasing tendency of early knock when the NO amount increases.