Technical Report 18, c4e-Preprint Series, Cambridge
Sources of emissions of CO and the Effects of Varying the Octane Number in an HCCI Engine
ref: Technical Report 18, c4e-Preprint Series, Cambridge
Associated Theme: Engines
We investigate the factors which influence a reliable prediction of CO emissions in a dual-fuelled, homogeneous charge compression ignition (HCCI) engine using an improved probability density function (PDF) based engine cycle model. A convective heat loss sub-model (based on a stochastic jump process) and a coalescence-dispersion approach have been included to account for inhomogeneities due to fluctuations, turbulent mixing and fluid-wall interactions. A base case comparison of the model predictions with the measurements (Olsson et al. SAE paper 2000-01-2867) suggests a good agreement between the model calculations and experimental results for auto-ignition timing, peak pressure as well as CO, HC and NOx emissions. Based on the model, fluidwall interactions, mixing of the hot and cold fluid parcels, and cylinder wall temperature have been identified to be critical for correctly predicting CO emissions, a task inherently difficult for the existing HCCI models in teh literature. Furthermore, the role of octane number in controlling (HCCI) combustion and emissions is investigated and the model predictions are compared with measurements. The auto-ignition timing and the in-cylinder pressure and emissions are observed to be sensitive to the variation in octane number. The magnitudes as well as the trends for the combustion parameters and the emissions (CO, HC and NOx) with respect to octane number are predicted reasonably well by the model.
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