Utilization of ICE exhaust gas as a heat source for pyrolysis of natural rubber as automobile fuel

Abstract

This research determined the gain of thermal efficiency of an internal combustion engine when its exhaust gas was utilized as a heat source for natural rubber pyrolysis. A 350-cc motorcycle engine was selected as a testing engine for carrying out the experiments. Its exhaust system was modified to have a pyrolyser fixed inside, and the exhaust heat was transferred through its surface toward the NR samples to cause pyrolysis. The exhaust port was designed to flare in order to reduce the exhaust velocity. Its static temperature was thus increased, which increased driving heat inside the pyrolyser. In case of determination of the NR pyrolysis rate, the NR samples were heated by the exhaust coming up by keeping the gear status at idle and setting an rpm value of 3200. The amount of the obtained NR pyrolysis products was plotted against time. Pyrolysis rates at each interval of time were determined and also plotted against the point of time, whereas the amount of gasoline consumed under the same interval of time was used to calculate the consumption rate. In the case of determination of the amount of heat recovery from the exhaust for the pyrolysis, a diffential scanning calorimeter-thermogravimetric analyser (DSC-TGA) hybrid was used as a pyrolyser instead of the modified engine, and the samples were run at the same temperature and under the same CO2 atmosphere as the engine did. The amount of the NR absorbed heat can be more precisely determined by using the DSC-TGA than by using the engine pyrolyser. Only the liquid fraction of the NR pyrolysis products, not gases, was collected and characterized by gas chromatography/mass spectrometry (GC/MS) and Fourier transform inflared spectroscopy (FTIR) techniques. The results show that the distilled NR oil contains plain C-H atoms of 97 wt. % and hydrocarbon with O atoms only 2.94 wt. %. This oil approximately contains 10 wt. % of the aliphatic chain and 87.4 wt. % of aromatic chain hydrocarbons. If the oil were supposed to feed back as the engine fuel, the thermal-efficiency gain of 0.43 percentage point could be obtained by the calculation, and the author believes that this would be the first IC engine that can consume solid fuel, i.e., natural rubber.