Investigation of combustion emissions in a HCCI engine-measurements and a new computational model

The CO and hydrocarbon emissions of a HCCI engine were elucidated by inhomogenieties in temperature-induced by the boundary layer and crevices according to a stochastic reactor model. The boundary layer consisted of a thin film and a turbulent buffer layer. The heat loss through the cylinder wall resulted in a significant temperature gradient in the boundary layer. Turbulent mixing between boundary layer, crevices, and the turbulent core was modeled using the Partially Stirred Plug Flow Reactor model. Natural gas combustion in the engine was described by a detailed chemical mechanism incorporated in the SRM. The turbulent mixing intensity describing the decay of the species and temperature fluctuations was estimated from measurements of velocity fluctuations and the integral length scale of the turbulent flow in the engine. CO emissions, pressure, and unburned hydrocarbons were also measured. Comparison between the mean quantities obtained from the SRM and these measurements showed very good agreement. SRM outperformed a previous PFR based one-zone model. The PaSPFR-IEM model captured the pressure rise which could not be described exactly using a simple one-zone model very well. CO and hydrocarbon emissions were also predicted well. Scatter plots of the marginal PDF of CO₂ and temperature showed that the emissions of hydrocarbons and CO could be explained by stochastic particles undergoing incomplete combustion because they are trapped in the colder boundary layer or in the crevices. Original is an abstract.