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The combustion of gasoline-air mixtures in a constant-volume combustion chamber with an initial condition of 0.1 MPa pressure and 363 K temperature is experimentally investigated with laser ignition generated by a Q-switched Nd:YAG laser (wavelengths of 532 and 1064 nm). Spark ignition is also tested, and the results are used as the benchmark. Combustion chamber pressure is measured by a piezoelectric pressure transducer, and recorded using a digital oscilloscope. When the equivalence ratio is swept from 1.2 to 1.8, laser and spark ignition show marginal differences in pressure rise rate and peak pressure. The maximum pressure rise rate and the maximum peak pressure are obtained at equivalence ratios of 1.6 and 1.8 for laser ignition and spark ignition, which are 39.4 MPa/µs and 0.68 MPa for the laser wavelength of 532 nm, 38.8 MPa/µs and 0.67 MPa for the laser wavelength of 1064 nm, and 38.1 MPa/µs and 0.67 MPa for spark ignition, respectively. When the equivalence ratio is reduced below 1.2, the pressure rise rate and peak pressure of the laser ignition are significantly higher than those of spark ignition, and the lean limit for laser ignition is also wider than that of spark ignition; therefore, laser ignition is more favorable for lean combustion. For both the laser and spark ignitions, the ignition energy demonstrated a limited impact on both the pressure rise rate and peak pressure. Heat release rate in the combustion chamber is calculated, and the results show that variations of heat release are in accordance with variations of the pressure history.

The ignition probability and minimum ignition energy (MIE) of premixed gasoline–air mixture for different equivalence ratio was experimentally studied using a nanosecond pulse at 532 nm and 1064 nm from a Q-switched Nd:YAG laser in a constant-volume combustion chamber (CVCC) The result was compared with the spark ignition. The initial pressure and temperature of the mixture was 0.1 MP and 363 K, respectively. The research indicates that within the flammable range, the probability increases when the ignition energy increases and the distribution of MIE with the equivalence ratios is U-shape for both laser and spark ignition. For laser ignition with 532 nm, when the incident energy is higher than 110 mJ or the absorbed energy is high than 31 mJ, 100% of ignition could be obtained within equivalence ratios of 0.8–1.6. For 1064 nm it is 235 mJ and 30 mJ. To get the same ignition probability of mixture with identical equivalence ratio, the incident energy of 1064 nm is twice more than the incident energy of 532 nm, while the absorbed energy values are virtually the same. It indicates that significant wavelength dependence is expected for the initial free electrons but irrelevant for the process of absorbing energy. The initial free electrons are produced from impurities in gasoline–air mixture because the intensity in the focus (10 12 W/cm 2 ) is too low to ionize gas molecules via the multi-photon ionization process, which requires higher irradiance (≥10 14 W/cm 2 ). The MIE obtained with a laser-spark ignition is greater than that measured by electrical sparks. The MIE for laser ignition was obtained at equivalence ratio of 1.0 both of 532 nm and 1064 nm, and it was 13.5 mJ and 9.5 mJ, respectively. But for spark ignition, the MIE is 3.76 mJ with equivalence ratio of 1.6. What׳s more, laser ignition extends the lean flammability limit from 0.8 to 0.6.

To solve the color cast of the night image, a color constancy algorithm using depth map to estimate the light source color is proposed. Firstly, the environment light source of night image is simulated by a single light source attenuated in homogeneous medium. Then, the attenuations grey hypothesis is used to provide constrain for estimate light source color. Based on the attenuations grey hypothesis and the simulation of environment light source, the light source color is estimated by the depth map. Experimental results show that the algorithm is effective to solve the color cast of the night image.