Use of hydrogen to enhance the performance of a vegetable oil fuelled compression ignition engine

Use of vegetable oils in unmodified diesel engines leads to reduced thermal efficiency and increased smoke levels. In this work, experiments were conducted to evaluate the performance while using small quantities of hydrogen in a compression ignition engine primarily fuelled with a vegetable oil, namely Jatropha oil. A single cylinder water-cooled direct-injection diesel engine designed to develop a power output of 3.7 kW at 1500 rev/min was tested at its rated speed under variable load conditions, with different quantities of hydrogen being inducted. The Jatropha oil was injected into the engine in the conventional way. Results indicated an increase in the brake thermal efficiency from 27.3% to a maximum of 29.3% at 7% of hydrogen mass share at maximum power output. Smoke was reduced from 4.4 to 3.7 BSU at the best efficiency point. There was also a reduction in HC and CO emissions from 130 to 100 ppm and 0.26-0.17% by volume respectively at maximum power output. With hydrogen induction, due to high combustion rates, NO level was increased from 735 to 875 ppm at full output. Ignition delay, peak pressure and maximum rate of pressure rise were also increased in the dual fuel mode of operation. Combustion duration was reduced due to higher flame speed of hydrogen. Higher premixed combustion rate was observed with hydrogen induction. Comparison was made with diesel being used as the pilot fuel instead of vegetable oil. In the case of diesel the brake thermal efficiency was always higher. At the optimum hydrogen share of 5% by mass, the brake thermal efficiency went up from 30.3-32%. Hydrocarbon, carbon monoxide, smoke emission and ignition delay were also lower with diesel as compared to vegetable oil. Smoke level decreased from 3.9 to 2.7 BSU with diesel as pilot at the optimum hydrogen share. Peak pressure, maximum rate of pressure rise, heat release rate and NO levels were higher with diesel than Jatropha oil. On the whole, it is concluded that induction of small quantities of hydrogen can significantly enhance the performance of a vegetable (Jatropha) oil/diesel fuelled diesel engine. © 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.