Abstract:
The broad objective of this research was to recover exhaust gases thermal energy from internal combustion engines for use in other applications. The specific objectives were: to determine the amount of thermal energy lost through exhaust gases at various engine speeds and loads; to determine the amount of energy recovered from exhaust gases at various engine speeds and loads; and to simulate the amount of maize that could be dried with the recovered energy. The experimental set-up consisted of a single cylinder, four-stroke, multi-fuel engine connected to an eddy current dynamometer for loading. Thermocouple temperature sensors and transmitters were used to measure exhaust gas to calorimeter inlet temperature and exhaust gas from calorimeter outlet temperature. Exhaust gas mass flow rate and temperature measurements were used to determine lost and recoverable energy. For purposes of estimating the amount of maize that could be dried with the recovered energy, safe and recommended temperatures were used. The dryer had a rated capacity of 1900 kg/h. The instrumentation of the engine was mainly equipped with a data acquisition system and ICE software. In general, fuel energy was observed to initially increase with engine speed and later decrease at higher speeds for both fuels at constant loads. For example, at 6 Nm fuel energy increased from 50295 kJ/h at 1000 rpm to 84945 kJ/h at 1250 rpm and later decreased to 64680 kJ/h at 1500 rpm for diesel fuel. The same trend was observed for biodiesel at a constant load of 6 Nm. At constant speeds, heat energy lost through exhaust gases increased with increased engine loading for both fuels. Recovered heat energy from exhaust gases increased with increased loading up to 18 Nm at speeds of 1000 rpm and 1250 rpm, but later decreased at a load of 22 Nm for both fuels. Heat energy could not be recovered at a speed of 1500 rpm and loads of 18 Nm and 22 Nm because calorimeter outlet temperatures of exhaust gases equaled inlet temperatures for both fuels. The specific energy required to dry maize from a moisture content of 25% to 13% wet basis was found to be 1124 kJ/kg. In this study, 750 and 566 grams per hour of maize could be dried through simulation when the engine used biodiesel and diesel respectively at an engine speed of 1000 rpm and a load of 18 Nm.
