It is a good solution to produce biodiesel by using waste edible oils (WEO), such as waste cooking oils and used frying oils, due to its low cost, disposal problems and potential contamination. Therefore, WEO biodiesels has been gradually produced, and thus applied to study their effects on engine performances and emissions. However, few reviews about these studies have been published to assist understanding and popularization for WEO biodiesels so far. This paper attempts to cite and analyze highly rated journals in scientific indexes about combustion characteristics, engine power, economy, regulated emissions and non-regulated emissions of WEO biodiesels on diesel engine. The use of WEO biodiesels leads to the slight difference in combustion characteristics such as ignition delay, rate of pressure rise, peak pressure and heat release rate, and the substantial reduction in PM, HC and CO emissions accompanying with the imperceptible power loss, the increase in fuel consumption and NOx emission on conventional diesel engines with no or fewer modification, compared to diesel. Although the inconsistent conclusions have been made on CO2 emission of biodiesels from WEO, it reduces greatly from the view of the life cycle circulation of CO2. For non-regulated emissions, the reduction appears for PAH emissions but carbonyl compounds emissions have discordant results for WEO biodiesels. Therefore, WEO biodiesels have the similar combustion characteristics, engine performances and emissions to that of biodiesels from food-grade oils, and the blends of WEO biodiesel with small content by volume could replace the petroleum-based diesel fuel to help in controlling air pollution, encouraging the collection and recycling of waste edible oil to produce biodiesels and easing the pressure on scarce resources to a great extent without significantly sacrificing engine power, economy and emissions.
