Establishing combustion temperature in a hydrogen-fuelled engine using spectroscopic measurements

The results reported in this article are based upon spectrographic measurements taken form, a single-cylinder hydrogen powered internal combustion engine. The goals, as stated by the US Department of Energy, are for hydrogen engines to achieve 45 per cent peak brake thermal efficiency, 0.07 g/mile NOx emissions, and US $45/kW. One of the primary research interests in hydrogen engines is to ensure operation of the engine without requiring NOx after-treatment. A reliable method to measure combustion temperature will be useful to achieve this goal. However, unlike most hydrocarbon combustion systems that emit soot radiation, hydrogen combustion provides little in the way of measurable radiation emission except for the excited state of the hydroxyl radical (OH*). An optical fibre was inserted into the cylinder head of this engine to capture the photons emitted by the OH* radical during combustion. Based upon the distribution of the intensity of photons emitted in the 306-310 nm band, the temperature of the OH* radical can be calculated. A computer algorithm was used to simulate the energy distribution. This simulated distribution is then compared with the measured distribution, iterating the simulation by change of temperature until it appropriately matches the measured distribution. This diagnostic also has potential application to combustion systems that also do not emit soot radiation; advanced low-temperature combustion concepts such as homogeneous charge compression ignition.