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

In engine development, it is needed to investigate engine performance under a lot of conditions. This is called the adaptability test, and it takes a lot of times, money, and manpower. Therefore, decreasing the test is aspired and constructing models that estimate the engine performance is effective for early adoption of ammonia engines. In this research, factors determining the thermal efficiency of a spark ignition engine fueled with ammonia/hydrogen mixtures were investigated and two simple models to estimate the performance were constructed. A diesel based four-stroke single-cylinder spark ignition engine with a displacement volume of 412 cm³ was used. Different compression ratios ε and two pistons with different squish areas were used. Experiments were conducted for total equivalence ratio of 1.0, while changing the LHV (lower heating value) ratio of ammonia and hydrogen. It is shown that higher compression ratio and larger squish velocity expanded the stable operation range of the engine. For high compression ratio with high squish piston, operation with pure ammonia was possible. The indicated thermal efficiency was expressed as a product of four factors; (i) the effect of compression ratio and specific heat ratio, (ii) the effect of change in molar number, (iii) the effect of degree of constant volume, and (iv) the combustion efficiency. Also, the indicated mean effective pressure was expressed as a product of four factors mentioned above and (v) the input heat. The model reproduced the measured indicated thermal efficiency and the measured indicated mean effective pressure in standard deviation of 0.03.