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Summary Hydrogen is one of the most promising alternative fuels for the transportation industry. The use of hydrogen to enable lean burn in internal combustion engines is an attractive solution for reducing CO2 emissions from two points of views: the substitution of carbon‐based fuels and the increased thermal efficiency due to lean operation. Combining this strategy with the passive pre‐chamber ignition system with gasoline/hydrogen blends is even more interesting. The main limitations of the passive pre‐chamber concept in a high compression ratio spark‐ignition engine were shown through engine experiments. A numerical study was then performed to evaluate the chance of extending the dilution limit by using hydrogen along with this technology. Results show how the use of hydrogen provides considerable benefits in the main chamber combustion process by enhancing the thermo‐chemical properties of the mixture, increasing the flame speed, and improving the flame structure. Using an adequate gasoline‐hydrogen blend proved to enable optimum burning rates at lean conditions, leading to a relevant thermal efficiency gain. [ABSTRACT FROM AUTHOR]

The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel-flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen-enriched methane were both experimentally and numerically investigated under ultra-lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one-step mechanism by Westbrook and Dryer and a two-step mechanism with an irreversible and reversible CO/CO2 step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under-predicted the temperature, major species, and NO x by more than 100% under ultra-lean conditions; thus, we proposed a modified-2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO2 emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over-predicted the NO x emission by approximately 81% and 152%, respectively, as compared with an average under-prediction of 11% by the modified-2sCM2 mechanism. The numerical results using the proposed modified-2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H2/CH4, there is an optimum equivalence ratio at which the pollutant emissions (CO and NO x) from the combustor are minimal. Zero CO and 5 ppm NO x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H2. The present study provides a basis for ultra-lean combustion toward achieving zero emissions from a fuel-flexible combustor. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]