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 (CI) 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. 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 deteriorate as the ambient temperature lowers. This is due to the physical and chemical properties of the transesterified vegetable oil derivatives, called "biodiesel".
In order to sustain this remark, the paper will present an experimental investigation regarding cold starting characteristics at -20 degrees C of a common automotive compression ignition engine using commercial diesel fuel and different blends of diesel oil with biofuel, such as B30, B40 and B50. The paper's final goal is to present a method of improving the cold startability by using a technique consisting in injecting some volatile substances of ether nature in the intake manifold. Discussions will be made on the implementation of the additional injector on the intake manifold as well as on the moment of injection and injection duration. Equally, the positive effects of this technique on startability will be outlined: increasing of real compression ratio and improving of auto-ignition process.
This work is 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, additional injector.