Abstract
Influence of boost pressure on combustion process and exhaust emission in controlled auto-ignition (CAI) engine was studied. The examinations were carried out using single-cylinder engine with fully variable valvetrain and gasoline direct injection. In order to achieve auto-ignition in-cylinder temperature was elevated with the use of internal gas recirculation (EGR) obtained via the negative valve overlap (NVO) technique. Fuel dilution obtained via increase of intake pressure resulted in substantial reduction of cylinder-out nitrogen oxides emission. However application of boosting resulted in excessive advance of auto-ignition timing and increase of pressure rate rise (PRR) at higher engine loads.
Highlights
A combustion system which utilizes controlled autoignition (CAI) of air-fuel mixture is nowadays one of the most promising solutions in the combustion engines development [1, 13]
Appearance of auto-ignition in numerous places in the combustion chamber simultaneously is a characteristic feature of CAI combustion system [8, 10]
Volumetric and low temperature combustion allows for 99% reduction of NOX emission in comparison to spark ignition of homogeneous mixture [3]
Summary
A combustion system which utilizes controlled autoignition (CAI) of air-fuel mixture is nowadays one of the most promising solutions in the combustion engines development [1, 13]. In-cylinder processes, which take place in a combustion chamber, are a combination of those typical of spark ignition and compression ignition engines. As a result of compression process in-cylinder temperature increases providing conditions for auto-ignition. In contrast to Diesel engines, air-fuel mixture is almost homogeneous. Appearance of auto-ignition in numerous places in the combustion chamber simultaneously is a characteristic feature of CAI combustion system [8, 10]. Volumetric and low temperature combustion allows for 99% reduction of NOX emission in comparison to spark ignition of homogeneous mixture [3]. Kinetic combustion results in fast heat release, thermal efficiency benefits from realization of close to ideal Otto cycle [6, 7]
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