Research Journal of Agricultural Science, 42 (1), 2010 630 IMPROVEMENT THE COLD START PROCESS OF IC ENGINES FUELED WITH BIODIESEL Florin MARIAŞIU, Bogdan VARGA The Technical University of Cluj-Napoca, ARMA Dept., Romania Corresponding author: Florin Mariasiu, e-mail: florin.mariasiu@arma.utcluj.ro Abstract: Even though currently the future use of biofuels in road transport (in terms of fossil fuel crisis) is much debated by specialists, biofuels can be successfully used on the farm by the ease with which they may be obtained and especially due to the effect polluter much lower than the fossil fuels. Reducing pollution from agriculture technological operations is a necessary condition to develop in the future agricultural development on a sustainable basis. To truly become a competitive fuel market, compared with fossil fuels, biofuels must optimize parameters related to characteristics of density, viscosity, freezing point and especially the specific calorific value. Global research about the efficient use of biofuels have emphasized only the immediate results of their use in supplying engines that equip tractors and agricultural machinery, related to consumption, pollution and wear of engines component parts. Theme and direction of research addressed in the paper represents an innovation in the field of national and global research on biofuels. Also, the degree of novelty of the work is defined by the methods and materials used in the research, managing to highlight first, the importance of parameters like speed of sound in biofuels (with subsequent implications in the possible development of "flex- fuel" systems) and isotropic adiabatic coefficient (with direct implications in determining the exact time of injection process). This paper presents findings related to the influence of external energy intake in the form of ultrasound, electromagnetic field and ionization on the physical parameters of biofuels (biodiesel and bioethanol), the main parameters considered are (speed of sound, density, isotropic adiabatic coefficient, pH index). Practical implications of the work are found in the immediate applicability in the possibility of increasing the performance of agricultural tractors powered by biofuels and also open new directions in applied research on ways of streamlining the use of biofuels. Results and conclusions issued in the work are possible due to the unfolding of the first phase of research project PNII2008ID175, financed by CNCSIS. Key words: biofuels, cold start process, ultrasounds, IC engine. INTRODUCTION It is known that diesel engines easy start depends directly by self-ignition quality and indirectly by cetane index, viscosity, fuel freezing and cloud temperature [1, 4]. In terms of behavior at low temperatures due to high amounts of vegetable oils cloud point temperature (+12 o …+30 o C) compared to diesel (-22 o ... 0 o C) some problems will appear related to flow through the injection pump (loss of engine power), clogging filters and supply lines [2]. Based on these considerations we can say that physical and chemical properties of biofuels have an important role on technical considerations related to their use in compression ignition engines [4,5]. Given that currently there is mainly machinery and vehicles that are equipped with engines built with older technology than that used in 2000, made technical changes to increase reliability as well as fuel engines to use vegetable oil (pure form or mixed form) must [2,3] :  to ensure the possibility of using alternative fuels in compression ignition engines in any season calendar;