Abstract
Historically, engine selection for light vehicles is about choosing either the spark ignition engine, with low initial cost and poor fuel economy or the compression ignition engine, with its high initial cost and good fuel economy. Of the two technologies, the diesel engine accounts now for more than 50% sales in Europe and that is explained by its low CO2 emissions and fun-to-drive feature, which, in their turn, are the result of the application of advanced technologies such as electronically controlled high pressure direct fuel injection, variable geometry turbocharging, multi-valves, charge motion control, etc. However, despite its improvements, the diesel engine still has problems at cold starting, which has negative effects on market acceptance and practical use. These problems are even greater for high specific power diesel engines as the higher the compression ratio within the air compressor, the lesser the engine volumetric compression ratio has to be, which will impair the cold startability. If adding the actual concern for the alternative fuels, the problem of the diesel engine cold starting becomes even more difficult when using biofuels. The cold starting characteristics of the biodiesel fuelled engine deteriorate as the ambient temperature lowers. This is due to the physical and chemical properties of the transesterified vegetable oil derivatives, called "biodiesel", which deteriorates the in-cylinder combustion.
Previous research has shown that startability degraded with increasing the percentage of biodiesel within the blends. In the present experimental research work, the effects of increasing the biofuel percentage on startability will be analyzed through the following data: instantaneous engine speed, instantaneous in-cylinder pressure and pressure rate, heat release and heat release rate. All these results will be analyzed on the cranking, stabilizing and idling stages in order to draw a conclusion about what happens when increasing the biofuel percentage.
The interest for this study is to create a referential and, afterwards, to see the effect of injecting some volatile substances (such as ether) within the intake manifold upon the cold starting with a large proportion of biodiesel of an engine featuring no glow plugs.
This work is, actually, carried out within the frame of a research project entitled "Research upon the development of a method to improve the cold starting of biodiesel engines for special destination vehicles", which is granted by the Romanian Council for Scientific Research in the Higher Education (CNCSIS).
KEYWORDS – biodiesel, cold start, in-cylinder pressure analysis