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Temperature distributions in n-heptane and n-tridecane sprays were measured by the planar laser induced fluorescence (PLIF) method. The spray was formed by injecting fuel into high temperature and high pressure ambient, which was formed by compression of rapid compression and expansion machine (RCEM). In this PLIF method, acetone was used as a fluorescence tracer and was mixed with ambient gas. The fluorescence tracer was excited by 266 nm (the 4th harmonic of a Nd:YAG laser). The fluorescence intensity was measured by an ICCD camera. The temperature and concentration were estimated based on temperature dependency of the fluorescence intensity and the assumption of adiabatic mixing. Based on the measurement results, The difference of mixture distributions in n-heptane and n-tridecane sprays are discussed.

As a result of the excavation of unconventional sources of natural gas, which has rich reserves, has attracted attention as a fuel for use in natural gas engines for power generation. From the viewpoints of efficient resource utilization and environmental protection, lean burn is an attractive technique for realizing a higher thermal efficiency with lower NOx emissions. However, ignition systems have to be improved for lean-burn operations. Laser ignition, which is expected to serve as an alternative to spark plug ignition, can decrease the heat loss and has no restriction on the ignition location because of the absence of an electrode. Consequently, an extension of the lean-burn limit by laser ignition has been demonstrated. In this study, we investigated the effects of the location and number of laser ignition points on engine performance and exhaust emissions. Laser ignition was also compared with conventional spark plug ignition.

We developed a novel ignition method called laser breakdown-assisted long-distance discharge ignition (LBALDI) that combines laser breakdown with a discharge to realize lean combustion. The creation of laser breakdown plasma between electrodes for discharge enables discharges over longer distances than those of conventional sparkplug as inferred from laser-triggered lightning or laser-triggered gas switches. This method should help realize volumetric ignition through the creation of a long-distance discharge. Experiments on the fundamental discharge and ignition of methane/air mixtures were conducted. The optimum incident time of the laser prior to the application of a high voltage was found to reduce the sparkover voltage and markedly reduce the voltage required by LBALDI under pressurized air conditions. In the ignition experiment, LBALDI showed the fastest heat release rate at the lean flammable limit.