Emissions from homogeneous charge compression ignition (HCCI) engine using different fuels: a review.

The main objective of this paper is to review the emission characteristics of homogeneous charge compression ignition (HCCI) engines using different fuels and additives. Additionally, the impacts of various operating conditions on HCCI engine emissions are also analyzed. There is a demand faced by the engine and car manufacturers for high fuel efficiency and low emission from both consumers and the government. HCCI is an alternative internal combustion technology that is more efficient and cleaner than traditional combustion techniques. In this engine, fuel and oxidiser (typically air) are entirely mixed and compressed to the point of auto-ignition. It is a new combustion concept that provides high efficiency and resolves high nitrogen oxide (NOx) and particulate matter (PM) emissions simultaneously. Conventional diesel engine emits NOx  around 2000-2500 ppm which is a primary concern; however, when diesel is used in HCCI engine, it reduces NOx to only 70-400 ppm. Furthermore, natural gas cannot be used as fuel in the conventional engine but can be used in HCCI engine. It helps reduce NOx emission even below 10 ppm. This paper reviews several works done by researchers on HCCI engines to reduce their emissions and benefit future research.