Browse Publications Technical Papers 2022-01-1062
2022-08-30

Comparison of a Laser Ignition with an Electrical Spark Ignitions System for Directly Injected Methane in a Rapid Compression Machine 2022-01-1062

As regulations regarding exhaust gas emissions of the internal combustion engine become more stringent, new concepts are necessary. The implementation of lean operation, direct injection to increase turbulence and facilitate stratified mixtures as well as methane as fuel in combination with high compression ratios can reduce exhaust gas emissions. Conventional electrical spark ignition systems reach their limits as higher pressures lead to faster erosion of the electrodes. Laser ignition profits from rising pressures at the time of ignition and has additional advantages such as the lack of electrodes leading to less heat dissipation and the possibility of arbitrarily positioning the ignition location. In this work results of experiments carried out in a rapid compression machine using directly injected methane to facilitate a partially stratified charge are presented. Two laser ignition systems based on Nd:YAG lasers with a wavelength of 1064 nm and pulse energies of 9.2 mJ and 12.3 mJ and different pulse durations are compared to a multispark transistor ignition system facilitating multiple ignition pulses. Two ultra-lean air-fuel equivalence ratios are investigated by evaluating the pressure curve, ignition probability, indicated work and the corresponding coefficient of variation. The novelty of the combination of all these aspects in an application oriented test bench with compression strokes provides numerous insights into the laser-initiated combustion. The results show an advantage of the laser ignition over the electrical system. The ignition probability for λ = 2.9 is higher for the laser ignition. For λ = 2.9, the pressure curves show higher maximum values for the laser system. For both air-fuel equivalence ratios the maxima appear earlier for the laser system indicating a faster combustion. The values of the indicated work for λ = 2.9 are higher for the laser system. The laser system obtains significant lower values for λ = 2.9 and λ = 3.1 regarding the coefficient of variation indicating a steadier combustion. Multiple pulses can improve the ignitions probability and reduce the cyclic variations but only for extremely short pulses.

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