Momentum flux-based model to estimate injection rate of an ammonia injector

Ammonia emerges as a feasible candidate to replace fossil fuels to avoid in-field CO2 emissions while operating low-speed internal combustion engines. An in-depth analysis of the injection process is necessary to enable the use of this fuel. The injection rate is a fundamental characteristic of the injection process, which describes the timing and instantaneous quantity of fuel mass introduced into the combustion chamber. However, the direct experimental evaluation of the injection rate is generally not possible due to the incompatibility of ammonia with existing measurement hardware. This study proposes a methodology to estimate the ammonia injection rate curve of high-pressure injectors for compression ignition engines based on momentum flux data, obtained using equipment suitable for ammonia properties. In this regard, two single-hole injectors were investigated using ammonia and, as a reference fuel, diesel. A comparison between the injection rate and momentum flux operating on diesel allows the derivation of a transfer function for extrapolating the injection rate curve from the momentum flux signal. After validating the model, it was applied to the case of ammonia injections for which only momentum flux data were available. The proposed methodology offers a viable alternative to obtain the injection rate measurement, particularly in challenging scenarios where only momentum flux data is available and direct measurement of the injection rate is not feasible.