A holistic evaluation of the impact of UK renewable strategy on emissions from compression ignition engines

Abstract

Reduction in fossil fuels, contributing to greenhouse gases, and improvement of air quality from vehicle emissions is of growing concern worldwide. This has led to the introduction of several binding and non-binding agreements, such as the Renewable Energy Directive to increase the renewable content of fuel for transportation, the carbon dioxide emissions standards to limit the amount of carbon dioxide emissions from vehicles and the Euro Standards to limit the amount of emissions harmful to human health in the exhaust. However, the influence of the fuel composition on hazardous exhaust emissions is a complex, and often contradictory, relationship between factors such as the fuel properties, combustion characteristics and engine load. Therefore policy implemented to improve one aspect, such as a reduction in carbon dioxide, can have a detrimental effect on another such as increased NOx emissions.This paper analyses, in a holistic manner, the impact on carbon dioxide and harmful emissions from transient compression ignition engines when increasing the renewable content of the fuel to meet the renewable energy targets. The analysis is based on a model developed from a rigorous Design of Experiment methodology used to determine the complex relationship between renewable fuel content and exhaust emissions (carbon monoxide, carbon dioxide and nitrogen oxides). Unlike other studies, the results were collected from a transient engine cycle, the World Harmonised Light vehicle Test Procedure, rather than steady state conditions, thus the results are more applicable to the real world.The results generally show that as the amount of ethanol is increased then the NOx and CO emissions decrease compared to current pump diesel. Increasing the biodiesel content generally increases the CO and CO2 emissions from the engine. For practical reasons a ternary blend is required to minimise the diesel engine emissions whilst meeting the UK’s future renewable content target. A blend of B2.4E10 was found to be the optimum compromise between renewable content and engine emissions. However, for this to be achieved the UK will have to invest in second and third generation ethanol.