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Effects of Gasoline-Air Enrichment with HRG Gas on Efficiency and Emissions of a SI Engine

Effects of Gasoline-Air Enrichment with HRG Gas on Efficiency and Emissions of a SI Engine

Radu Chiriac, Nicolae Apostolescu

University POLITEHNICA of Bucharest

Corneliu Dica



The addition of hydrogen to the gasoline-air mixture may contribute significantly towards accelerating the combustion process, with the beneficial effects on engine performance and emissions.

The present contribution describes the results of an experimental research where gasoline-air mixture was enriched with a Hydrogen Rich Gas (HRG) produced by the electrical dissociation of water. The HRG analysis shows the presence of hydrogen and oxygen together with some additional species.

Experiments were carried out at engine light and partial load. Detailed results of the measurements are shown, namely engine torque and efficiency, exhaust emissions, cyclic variability, heat release rates and combustion duration. The possibilities of improving engine performance and emissions in correlation with the amount of HRG, the equivalence ratio and the engine operating condition are thus outlined.


  • The effect of additions of HRG on gasoline combustion has been experimentally investigated in a passenger car engine. It was shown that:
  • The addition of HRG has a positive effect of combustion process enhancement. BTE, NIMEP, and (COV)NIMEP are improved, in connection with the combustion duration shortening. HC and eventually CO emissions concentrations are also reduced, while NOX is generally increased. The maximum lambda value (1.20) was a limit imposed by engine running stability.
  • The effect of HRG addition is most apparent at light load with leaned mixtures.
  • The effect of HRG addition was explained in terms of well known influence of hydrogen, the main component of HRG. A possible influence of other species existing in the gas was yet not identified.
  • Hydrogen and oxygen mixtures are very reactive and represent a potential hazard of pre-ignition, if an ignition source is present (static electricity). In this sense, experiments are continuing with the HRG direct injection in the cylinder.

Both, experiments and simulations have shown the possibility of a significant gasoline fuel consumption reduction obtained from hydrogen addition. The total efficiency improvement can be considered as the result of several effects: the partial de-throttling because the hydrogen, which has a low density, decreases the amount of air filling the cylinder; the faster combustion, thus approaching the ideal Otto cycle; the possibility to increase the compression ratio due to a higher resistance to knock.

Read the complete report: Effects of Gasoline-Air Enrichment with HRG Gas on Efficiency and Emissions of a SI Engine _SAE_Paper_2006-01-3431

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