Performance of the Mixture of Ammonia and Ammonia Decomposition Products as a Carbon-Free Fuel for Spark Ignition Engines

This work is devoted to assessment of the reactivity of the ammonia-based mixed fuels consisting of ammonia and products of its decomposition to hydrogen and nitrogen. For these purposes the thermodynamic, chemical kinetics and engine cycle simulations are performed. The dependence of the mixed fuels laminar flame speed, which is a measure of fuel reactivity, on ammonia decomposition degree is obtained. It is shown, that if about 37% of ammonia are decomposed and mixed with remaining ammonia (either hydrogen/nitrogen or pure hydrogen), then the reactivity of obtained mixture is similar to that of natural gas in a wide range of conditions. The engine performance parameters are estimated and compared for two fuels with the similar reactivity: natural gas or ammonia-based mixed fuels. It is shown, that the reduction of engine power by 8% is obtained when transferring from natural gas to considered ammonia-based mixed fuel. Reduction of NO_x emissions is about 50% due to lower combustion temperature of the mixed fuel. Further studies imply the assessment of the engine knock limits for proposed ammonia-based mixed fuels, as well as assessment of the ammonia decomposition process effect on overall engine performance and operability limits.