Major sources of hydrocarbon emissions in a premixed charge compression ignition engine

• Published in: International journal of automotive technology Vol. 13; no. 3; pp. 347 - 353
• Main Authors: Jung, G. S., Sung, Y. H., Choi, B. C., Lee, C. W., Lim, M. T.
• Format: Journal Article
• Language: English
• Published: Heidelberg The Korean Society of Automotive Engineers 01.04.2012; Springer Nature B.V; 한국자동차공학회
• Subjects: Analysis; Automotive Engineering; Carbon monoxide; Emissions; Engineering; Engines; Hydrocarbons; Studies; 자동차공학; Piston top-ring crevice; Quench distance; Exhaust hydrocarbon emissions; Intake air heating; Crevice volume; PCCI (Premixed Charge Compression Ignition); Bulk quench
• ISSN: 1229-9138; 1976-3832
• DOI: 10.1007/s12239-012-0032-5

Although premixed charge compression ignition (PCCI) combustion engines are praised for potentially high efficiency and clean exhaust, experimental engines built to date emit more hydrocarbons (HCs) and carbon monoxide (CO) than the conventional machines. These compounds are not only strictly controlled components of the exhaust gas of road vehicles but are also an energy loss indicator. The prime objective of this study was to investigate the major sources of the HCs formed in the combustion chamber of an experimental PCCI engine in order to suggest some effective technologies for HC reduction. In this study, to explore the dominant sources of HC emissions in both operation modes, a single cylinder engine was prepared such that it could operate using either conventional diesel combustion or PCCI combustion. Specifically, the contributions of the top-ring crevice volume in the combustion chamber and the bulk quenching of the lean mixture were investigated. To understand the influence of the shape and magnitude of the crevice on HC emissions, the engine was operated with 12 specially prepared pistons with different top-ring crevices installed one after another. The engine emitted proportionally more HCs as the depth of the crevice increased as long as the width remained narrower than the prevailing quench distance. The top-ring-crevice-originated exhaust HCs comprised approximately 31% of the total HC emissions in the baseline condition. In a series of tests to estimate the effects of bulk quench on exhaust HC emissions, intake air was heated from 300K to 400K in steps of 25K. With the intake air heated, HC and CO emissions decreased with a gradually diminishing rate to zero at 375K. In conclusion, the most dominant sources of HC emissions in PCCI engines were the crevice volumes in the combustion chamber and the bulk quenching of the lean mixtures. The key methods for reducing HC emissions in PCCI engines are minimizing crevice volume in the combustion chamber and maximizing intake air temperature allowed based on the permissible NOx level.