Technical Report 24, c4e-Preprint Series, Cambridge
Analyzing the limits of a stable Homogeneous Charge Compression Ignition (HCCI) operation
ref: Technical Report 24, c4e-Preprint Series, Cambridge
Associated Theme: Engines
We present a computational tool to develop an operating window for a homogeneous charge compression ignition (HCCI) engine. A single cylinder Ricardo E-6 engine running in HCCI mode with external exhaust gas recirculation (EGR) is being simulated using an improved probability density function (PDF) based engine cycle model. For a base case, the in-cylinder temperature and unburned hydrocarbon emissions predicted by the model show a satisfactory agreement with measurements [Oakley et al., SAE Paper 2001-01-3606]. Furthermore, the integrated model is applied to develop the engine operating window for various combustion parameters, emissions and engine parameters with respect to the air-fuel ratio and the amount of EGR used. The model predictions agree reasonably well with the experimental results for various parameters over the entire operating range thus proving the robustness of the PDF based model. The boundaries of the operating window namely, knocking, partial burn, and misfire are reliably predicted by the model. In particular, the model provides a useful insight into the misfire phenomenon by depicting the cyclic variation in the ignition timing and incylinder pressure profiles. Finally, we investigate two control options, namely heating intake charge and trapping residual burnt fraction by negative valve overlap. The effect of these two methods on HCCI combustion and CO, HC and NOx emissions is studied.
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