Boosting for High Load HCCI

Homogeneous Charge Compression Ignition (HCCI) holds great promises for good fuel economy and low emissions of NO_X and soot. The concept of HCCI is premixed combustion of a highly diluted mixture. The dilution limits the combustion temperature and thus prevents extensive NO_X production. Load is controlled by altering the quality of the charge, rather than the quantity. No throttling together with a high compression ratio to facilitate auto ignition and lean mixtures results in good brake thermal efficiency. However, HCCI also presents challenges like how to control the combustion and how to achieve an acceptable load range. This work is focused on solutions to the latter problem.

The high dilution required to avoid NO_X production limits the mass of fuel relative to the mass of air or EGR. For a given size of the engine the only way to recover the loss of power due to dilution is to force more mass through the engine. This paper shows that this can be done by the use of turbo charging or a mechanically driven compressor. The cost of forcing more air through the engine and the higher peak pressure requirements are discussed and quantified by simple engine modeling supported by experimental data.