Review of Regulated, Unregulated and Particulate Emissions from Biodiesel Fuelled Compression Ignition Engines

Compression-ignition (CI) engines have been utilised in transport and power generation sectors due to their excellent thermal efficiency, robustness and durability. However, the rapid depletion of crude oil reserves and environmental concerns have forced CI engines to be powered by alternative and environment-friendly renewable fuels. Biodiesel, which contains similar to 10 % (w/w) oxygen in its fuel molecules, has become a popular alternative fuel for CI engines. Biodiesel can be stored similar to mineral diesel. Hence it does not require a separate fuel distribution infrastructure. The fuel properties of biodiesel are very close to mineral diesel; hence conventional CI engines can be fueled with biodiesel/blends without major modifications in the engine hardware/software. It is also widely known that biodiesel in CI engines brings significant benefits of lower emissions such as unburned hydrocarbons, carbon monoxide, and particulate matter (PM). Since biodiesel is considered an attractive alternative fuel, there are many attempts to produce and utilise biodiesel in different applications from various feedstocks such as soybean, rapeseed, and waste cooking oil. Hence, it is necessary to understand the effects of biodiesel feedstocks and engine applications (operating conditions, engine type, etc.) on regulated and unregulated emissions. This paper reviews effects of biodiesel on regulated/unregulated/particulate matter (PM) emissions based on numerous experimental research studies in open literature conducted on a variety of engines using different biodiesels.