Performance and emissions of a CRDI diesel engine fuelled with swine lard methyl esters–diesel mixture

Abstract

Biodiesel, as a product of the transesterification reaction of fatty material, is gaining appreciation all over the world and confirms its beneficial effect on the reduction of exhaust gases when (even partly) used to power compression-ignition engines. Although many researchers have focused on biofuel production and its application in combustion engines, continuous development of injection systems, providing new control strategies, encourages the seeking for new ways of optimizing biofuel combustion. In particular, very little attention has been given to the possibility of using biofuels in modern CRDI (Common Rail Direct Injection) engines with divided injection technology. There is also limited information available on engines operating on biodiesel of animal origin and their performance and emissions for such fuels.Because of this gap of knowledge, in the present study, the authors focused on analysing the phenomena of combustion of animal-origin biodiesel mixtures in a CRDI engine. Swine lard methyl esters, obtained in the laboratory by a single-step alkali transesterification process as a biocomponent, and mineral diesel were used to obtain B25, B50, B75 mixtures (25%, 50% and 75% of biocomponent concentration by volume). The physicochemical parameters of B25, B50, B75, pure esters and mineral diesel were examined to determine whether the fuels met quality standards. The mixtures were used to fuel a 2.6L Andoria CRDI engine placed on a dynamometer test stand. Tests were carried out in steady state operation, at rotational speeds when two different injection strategies occur (single injection and two subsequent injections), also different load conditions were introduced during tests. During the tests, engine performance and exhaust gas emissions were measured and analysed in detail.The study has confirmed the capability of using diesel–biodiesel mixtures containing up to 75% biocomponents in a modern CRDI engine without any operational issues. A minor deterioration of fuel performance parameters with an increasing biodiesel share has been observed. Brake-specific fuel consumption increased on average by 3.2%, 8.5% and 13.8% for B25, B50 and B75, respectively. An average reduction of brake fuel conversion efficiency was observed, amounting to 1.6%, 4.8% and 7.8% for B25, B50 and B75, respectively. Significant reduction of exhaust gas emissions (excluding NOx) and opacity was also observed in all examined operation conditions. Total hydrocarbon concentration was reduced by a maximum of 72% for the B75 mixture for a speed of 1500RPM and 100Nm load. The best emission performance was observed for operation conditions when a short pre-injection occurred early in the compression phase, before the main fuel injection. This has proven that advanced injection strategies can be applied to fuel mixtures with high biodiesel share, especially for low engine load conditions.