IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 14, Issue 3 Ver. VII. (May - June 2017), PP 08-12 www.iosrjournals.org DOI: 10.9790/1684-1403070812 www.iosrjournals.org 8 | Page Comparison of Thermal Energy Lost through Exhaust Gases at Various Engine Speeds and Torque Loads for Diesel and Biodiesel Fuels George Orido 1 , Prof. Godfrey Ngunjiri 2, Dr. Musa Njue 3 1 (Agricultural Engineering/ Egerton University, Kenya) 2 (Agricultural Engineering/ Egerton University, Kenya) 3 (Agricultural Engineering/ Egerton University, Kenya) Abstract: This paper compares amount of thermal energy lost through exhaust gases when an engine was operated on diesel and biodiesel. The study used a 4.7 hp (3.5 kW) single cylinder, four-stroke, multi-fuel engine which was operated on diesel and biodiesel fuels. Experiments were conducted for the two fuels at engine speeds of 1000, 1250 and 1500 rpm in accordance with the manufacturer’s recommendations. The e ngine was tested for torque loads of 6 to 22 Nm at intervals of 4 Nm for speeds and fuels studied. The instrumentation of the engine was mainly equipped with data acquisition system and software for analysis. Exhaust gas mass flow rate and temperature measurements were used to determine lost thermal energy. Lost heat energy depended on the temperature of the waste heat gases and mass flow rate of exhaust gas. The energy lost in exhaust gases increased substantially with increased exhaust gas temperature. The results showed that more energy was lost through exhaust when the engine used biodiesel as compared to when it was fueled on diesel. Maximum heat loss through exhaust was 18.7% of fuel energy when the engine used biodiesel at a speed of 1500 rpm and a torque load of 14 Nm. Keywords: Engine Speed, Enthalpy, Exhaust Gases, Thermal Energy, Torque Load I. Introduction Exhaust gases immediately leaving the engine can have high temperatures. Consequently, these gases have high heat content, carried away as exhaust emission. In general, diesel engines have an efficiency of about 35% and thus the rest of the input energy is wasted. Despite recent improvements of diesel engine efficiency, a considerable amount of energy is still expelled to the ambient with the exhaust gas. The mass flow rate of exhaust gas is a function of the engine size and speed, hence the larger the engine size and the higher the speed, the more the exhaust gas heat. Compared to the composition of air, the diesel exhaust gas contains increased concentrations of water vapour and carbon dioxide. These are the main combustion products. The concentrations of both water vapour and carbon dioxide can vary from a few percent, up to about 12% in diesel exhaust. These combustion products displace oxygen, the concentration of which can vary from a few percent, up to about 17% (compared to 21% in ambient air). The main component of diesel exhaust, just as is the case with ambient air, is nitrogen [1]. By comparison, the concentrations of diesel exhaust pollutants are very small and for the purpose of calculating the physical properties of diesel exhaust gas, they can be neglected. Moreover, studies on total energy distribution from an internal combustion engine has shown that out of the possible 100% fuel energy content in an engine, 35% is useful as brake power, 30% is lost in the cooling system, 5% is lost through radiation and approximately 30% is lost through the engine exhaust [2]. As an approximation, the properties of air can be used for diesel exhaust gas calculations. The error associated with neglecting the combustion products is usually no more than about 2%. In a more rigorous approach, corrections must be taken to account for the actual exhaust gas composition (increased water vapour and carbo dioxide, decreased oxygen). An additional difficulty with this approach is the necessity to account for the variable exhaust gas composition, which changes with the engine load factor and the air-to-fuel ratio [3]. Physical properties of mixtures of gases, and methods to calculate them from the properties of components can be found in the literature [4]. In addition to the physical properties, knowledge of certain other exhaust gas parameters is important. These include exhaust gas temperature which is of special importance for the design of catalytic after treatment devices, as catalyst performance is a function of temperature and exhaust gas flow rate. Another important parameter is the maximum pressure drop through the exhaust system, caused by the hydraulic resistance of exhaust system components. This parameter, commonly referred to as the “engine backpressure” requires that the engine perform additional pumping work, and has other impacts on engine operation. In the light of the above discussion based on introduction, it is hoped that this paper on lost thermal energy will make some contribution to existing knowledge in the wide and ever changing field of engineering. In addressing the knowledge gap, the paper seeks to propose a study on efforts to design more energy efficient engines with better