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Reliable initiation of flame kernel development by an electrical spark in IC engines operating at ultra-lean air-fuel mixtures lays down specific demands to spark discharge variables. The demands become especially strict under conditions of intensive mixture motion through the spark gap. The main goal of this study was to determine experimentally the minimum values of spark duration and spark current in the glow phase of the discharge necessary for reliable ignition of methane-air mixtures with equivalence ratios of 0.7 down to 0.6. Different combinations of flow velocity and spark plug orientation with respect to mean flow vector have been considered. A special experimental ignition system was employed to set up spark discharge variables. Besides, a numerical study of early flame kernel development under conditions used in the tests has been carried out.

Flash boiling occurs when a liquid which initially is in a subcooled state, rapidly depressurized to a pressure sufficiently below saturation pressure to initiate a rapid boiling process. This phenomenon can be applied to improve fuel atomization in spark-ignition engines. In the present work, the characteristics of the generated spray were investigated experimentally. This is in order to establishing a designer guideline, for this high potential type of fuel injectors. The following conclusions have been derived: 1. A typical droplets Sauter mean diameter in the range of 20-40μm can easily be achieved with the present simple fuel injection system. 2. The SMD decreases with the increasing in the mole fraction of the propellant; at high pressure however (high propellant content), the SMD is less and less affected. 3. The SMD and the droplets' uniformity are independent of the orifices' size. 4. The SMD increases with the axial distance. 5.

The relationship between the characteristics of a spray pattern that is generated by a simple external-mixing plain-jet atomizer, in pulse mode, and the control parameters of the injection system, has been investigated experimentally. The experimental conditions varied in the range of Re=1236 to 3540, We=65 to 595, and air/liquid velocity ratio from 15 to 110. The pulse duration varied between 3.4 and 18.5ms. It was found that, 1. the Sauter mean diameter is proportional to (Vf/Va3)0.5 over the entire range of operational conditions (within an error of ±7.5%), 2. a shorter pulse and a longer time interval between the pulses result in a smaller SMD, 3. the SMD may by decreased by some 25%, as compared to a continuous injection, when the pulse time duration reduces to 20% of the total cycle time, and 4. short time pulses and long interval between pulses, are always preferable to produce small droplets.

Cyclic Variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. Previous studies have shown that if cyclic variability could have been eliminated, there would be a 10% increase in the power output for the same fuel consumption. The cyclic variability results also in high level of variations in the engine speed which is interpreted as poor driveability. At full load, some of cycles tend to knock, while other may not have complete combustion by the time the exhaust valve opens. An experimental study has been performed in order to evaluate the relative contribution of several relevant parameters on the cyclic variability in spark ignition engines. The cyclic variability has been examined via five major different pressure-related identifier, i.e. Pmax, θPmax, IMEP, (dp/dθ)max and θ(dp/dθ)max.

Cycle variability in spark-ignition engines is mainly attributable to the occurrence of poor ignited and misfired cycles. The non-ordinary ignited cycles were previously observed to occur when either, the flame did not move away from the electrodes, and therefore had much contact with electrodes, or when large portions of the flame were rapidly convected away from the electrodes and therefore the flame was quenched in the flow field. Cycle variability can also occur due to turbulence or non-homogeneity in the mixture strength. Experiments showed that the degree of the cyclic variability depends very much on the characteristics of the introduced spark, the flow regime in the electrodes' gap, and the spark plug design. In the present work, we investigated the effect of the amount of energy supplied to the spark plug, the law of energy deposition during glow phase, the mean velocity vector in the spark gap and the spark plug orientation, on the mixture lean misfire limit.