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Effect of H2/O2 addition in increasing the thermal efficiency of a diesel engine

Effect of H2/O2 addition in increasing the thermal efficiency of a diesel engine

S. Bari *, M. Mohammad Esmaeil

Sustainable Energy Centre, School of Advanced Manufacturing and Mechanical Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia


Using hydrogen as an additive to enhance the conventional diesel engine performance has been investigated by several researchers and the outcomes are very promising. However, the problems associated with the production and storage of pure hydrogen currently limits the application of pure hydro- gen in diesel engine operation. On-board hydrogen–oxygen generator, which produces H2/O2 mixture through electrolysis of water, has significant potential to overcome these problems. This paper focuses on evaluating the performance enhancement of a conventional diesel engine through the addition of H2/O2 mixture, generated through water electrolysis. The experimental works were carried out under constant speed with varying load and amount of H2/O2 mixture. Results show that by using 4.84%, 6.06%, and 6.12% total diesel equivalent of H2/O2 mixture the brake thermal efficiency increased from 32.0% to 34.6%, 32.9% to 35.8% and 34.7% to 36.3% at 19 kW, 22 kW and 28 kW, respectively. These resulted in 15.07%, 15.16% and 14.96% fuel savings. The emissions of HC, CO2 and CO decreased, whereas the NOx emission increased.


The impacts of using a small amount of H2/O2 mixture as an additive on the performance of a four-cylinder diesel engine were evaluated. The required amount of the mixture was generated  using electrolysis of water considering on-board production of H2/ O2 mixture. Hydrogen which has about nine times higher flame speed than diesel has the ability to enhance overall combustion generating higher peak pressure closer to TDC resulting in more work. The experimental results showed that with the introduction of 6.1% total diesel equivalent H /O mixture into diesel, the brake thermal efficiency increased by 2.6% at 19 kW, 2.9% at 22 kW, and 1.6% at 28 kW. The brake specific fuel consumption of the engine reduced by 7.3%, 8.1%, and 4.8% at 19 kW, 22 kW, and 28 kW, respectively. However, adding H2/O2 beyond 5% does not have sig- nificant effect in enhancing the engine performance. The emissions of HC, CO2 and CO were found to be reduced due to better combus- tion while NOx increased due to the higher temperature reached during the combustion.

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