On the possibilities to reduce compression ignition engine emissions by controlling the reactivity of diesel-biofuel mixtures

Abstract

In most European countries the use of different biodiesel fuels has been proved to be a sustainable method to reduce the pollutant emissions of the operating Diesel engines. An in-debt analysis of combustion characteristics is necessary to give a detailed perspective on the advantages of biodiesel use in compression ignition engines. Among all the essential parameters characterizing the compression ignition engine operation, the ignition delay is the most difficult to be estimated. This parameter offers the possibility to have more control over the combustion process inside the cylinder. This gives the ability to better quantify and ultimately to decrease the pollutant emission for this type of engine. An experimental study has been conducted on a tractor Diesel engine using different biofuel mixtures with 7% and 20% volumetric fractions of fatty acid methyl esters in Diesel fuel. No modifications were made to the fuel injection system in order to have a better image of the direct impact of biodiesel fuel on performance and emissions of the engine. The obtained results showed some reductions of total unburned hydrocarbons and nitrogen oxide emissions over the entire engine speed domain for both tested biodiesel fuels. The estimation of the ignition delay was experimentally carried out and correlated with the properties of the biodiesel fuel; a proper control of the combustion process by fuel reactivity ensured thus the mitigation of carbon monoxide, carbon dioxide and smoke. The link between the experimentally determined ignition delay, mainly it’s reduction, and fuel reactivity is what the present work tries to analyse. A better evaluation of the ignition delay parameter, shorter when using biodiesel mixtures, should lead to better control of combustion and further lowering the exhaust pollutant emissions, without major impact on engine performance. An in-debt analysis of the combustion process starting from the injection characteristics correlated with the fuel reactivity is necessary for shortening the ignition delay and reducing carbon dioxide emissions.