A comparison of life-cycle emissions of liquid biofuels and liquid and gaseous fossil fuels in the transport sector

Abstract

It has been claimed that the use of transport fuels such as compressed natural gas (CNG) and liquefied petroleum gas (LPG) leads to reduced greenhouse gas emissions compared to the conventional petroleum transport fuels, motor spirit and automotive diesel fuel. While it is certainly true that the ‘tailpipe’ greenhouse gas emissions during combustion of CNG and LPG are lower per km travelled than those of motor spirit and diesel, on a full ‘well to wheel’ life-cycle analysis there is little if any difference due to the high processing overheads involved in the production of CNG and LPG. If the fugitive emissions that may occur during CNG and LPG production, transmission and use are also taken into account, then their total greenhouse gas emissions per GJ or per km travelled may actually be considerably higher than those of motor spirit and diesel. On the other hand, the use of biofuels such as triglyceride esters and ethanol may lead to lower lifecycle greenhouse gas emissions. This paper examines some of the issues relating to the life-cycle emissions of various petroleum fuels, gaseous fuels and biofuels and provides a brief review of recent research in this area