Abstract
This paper presents a description of the main results related to experiments performed using biodiesel. The biodiesels were obtained from different feedstocks (soybean, palm, rapeseed and Jatropha Curcas). The results cover in a first part the physico-chemical analyses based on gas chromatography and thermal analysis, as well as kinematic viscosity. The second part of the paper is a discussion about the engine tests carried out with the biodiesels and a comparison with the results obtained for standard diesel fuel. The engine bench tests cover power output, torque, specific fuel consumption (SFC), ignition delay and exhaust gas analysis. Concerning the chemical analysis, significant differences in the Fatty Acid Methyl Esters (FAME) composition were observed among the biodiesel samples. Important differences in FAME among a genetic diversity of Jatropha (JC) species were found. The thermogravimetric analysis for soybean, palm and rapeseed oil biodiesel showed similar thermal profiles, but different from the Jatropha derivate’s profiles. All the biodiesels tested showed thermal decomposition processes that begin and end at higher temperatures compared to diesel fuel’s thermal profile. The bench tests showed a decrease in the engine performance using biodiesel compared to diesel fuel and no significant differences among the biodiesels. In all the experiments, a shorter ignition delay when biodiesel is used was observed. Correlations to predict ignition delay as a function of cylinder pressure and temperature from the engine tests and including theoretical calculations were developed. An increase in NOx emissions for biodiesel tests was observed related to the higher temperatures in the combustion chamber when biodiesel is used. The main conclusions of this research are: the composition of the biodiesels tested are strongly influenced by the feedstock and soil characteristics. The thermal decomposition process of biodiesel from JC is different from the other tested biodiesels. Important variations in engine performance when biodiesel is used are observed compared to diesel fuel, involving power output, SFC, ignition delay and emissions.
A shortening in ignition delay is generally observed when biodiesel is used due to its higher cetane number. The ignition delay correlations obtained show a better prediction capability than other previously reported correlations for diesel fuel.
KEYWORDS: biodiesel, performance, ignition delay, Jatropha, FAME.