Effects of using renewable fuels on vehicle emissions

In an effort to reduce greenhouse gas emissions, renewable fuels (biofuels) are being developed and used in motor vehicles. The most common of these are bioethanol and biodiesel that are blended with petroleum based gasoline and diesel fuels at varying percentages. This provides some reduction in the fossil carbon emissions from these fuels. Biomethane (produced from biogas) can and is used as a vehicle fuel to a much more limited extent. Significant modifications are required for the motor vehicle to use biomethane. The use of bioethanol blended fuels leads to increases in emissions of formaldehyde and acetaldehyde, with an accompanying decrease in benzene emissions. Nitrogen oxides (NOx) emissions are often increased with the use of bioethanol. The use of biodiesel blended fuels generally leads to increased NOx emissions, and decreases in particulate matter (PM) emissions. The use of biomethane is expected to have little adverse impact on the emissions from the combustion process, but it will lead to increased emissions of methane due to leakage and unburned fuel emissions. Methane is a stronger greenhouse gas than CO2, which is the greenhouse gas emitted in largest quantities from all combustion processes. With the appropriate time and effort, operating and emission control technologies can be developed to minimize the adverse effects that biofuel use will have on vehicle emissions. But this will require that vehicles be properly designed for the use of specific biofuels or biofuel blends. Renewable fuels may lead to decreases in greenhouse gas emissions, even with increasing use of transport fuels. No improvement, and more likely deteriorating air quality, is expected in the future with increasing renewable fuel use. (C) 2015 Elsevier Ltd. All rights reserved.