Development of Simple Models for Performance Estimation of a Spark Ignition Engine Fueled with Ammonia and Hydrogen

Achieving a carbon neutral society, eliminating greenhouse gas emissions is one of the most important issues. Ammonia is expected as a carbon free energy source. However, the laminar burning velocity of ammonia is much slower than hydrocarbons. Then, it is common to reform a portion of ammonia and use the ammonia/hydrogen mixture as a fuel. In this research, the operating characteristics of spark-ignition engine fueled with ammonia reformed gas is investigated and construct model estimating engine performance. A four-stroke single cylinder spark-ignition engine with a stroke volume of 212 cm3 is used. Total equivalence ratio is kept at unity and ammonia equivalence ratio is changed. Also, ammonia reformed gas is simulated as follows: ammonia and hydrogen are supplied from high pressure cylinders and injected by using automobile gaseous fuel injectors. Nitrogen is supplied from high pressure cylinder and supplied 1/3 of the molar ratio to hydrogen by a mass flow controller. The test engine is connected to a generator, and power generated is consumed using resistors. A portion of engine exhaust gas is heated and diluted, and the concentration of ammonia, NO, NO2, N2O are measured by using a QCL-IR. Results show that increasing ammonia equivalence ratio reduces the coefficient of variation of Indicated Mean Effective Pressure (COV of IMEP). This is because the burning velocity of ammonia is small, and this causes making flame kernel and the flame propagation difficult. Then, the indicated thermal efficiency goes down and unburnt ammonia emissions increase. Indicated thermal efficiency is affected by heat release rate. Heat release rate is expressed with Wiebe function. The concentration of unburnt ammonia is estimated by the volume of the quenching layer. NO emissions are almost independent of the ammonia equivalence ratio. Also, N2O emissions remain at low concentrations under all conditions.