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This paper describes a computer simulation of Diesel spray formation and the locations of self-ignition nuclei. The spray is divided into small elementary volumes in which the amounts of fuel and fuel vapours, air, mean, maximum and minimum fuel droplet diameter are calculated, as well as their number. The total air-fuel and air-fuel vapour ratios are calculated for each elementary volume. The paper introduces a new criterion for determining self-ignition nuclei, based on assumptions that the strongest self-ignition probability lies in those elementary volumes containing the stoichiometric air ratio, where the fuel is evaporated or the fuel droplet diameter is equal to or lower than 0.0065 mm. The most efficient combustion in regard to consumption and emission will be in those elementary volumes containing stoichiometric air ratio, and fuel droplets with the lowest mean diameters. Measurements of injection and combustion were carried out in a transparent research engine.

The paper presents the results of liquid fuel radial distribution measurements of 25 different spray cross-sections at various distances from the injection nozzle. The measurements showed that fuel drops, sprayed into the air, evaporated and the spray diameter increased. The calculation of evaporated fuel quantity was based on the volume of injected fuel and the amount of liquid fuel measured in each spray cross-section. For the purpose of measuring the liquid fuel in a spray we developed a device using ring electrodes to measure electric charge of the fuel, resulting from fuel rubbing against the injection nozzle metal parts and the measuring device electrodes. The temperature gradient in the ring electrode is caused by droplets hitting it at the velocity of 100 to 300 m/s. Their kinetic energy is instantly transformed into the thermal energy the consequence of which is the temperature gradient in the ring electrode.

The paper deals with the optimisation process of existing engines and the compilation of data to allow future electronic control of fuel injection. The general trend is towards the development of high-pressure electronic injection with injection pressures exceeding 1500 bar and with the reduced injection timing. We based our research measurements of diesel engine on the above assumptions. The measurements were undertaken on an engine tester by means of an analyser, charge amplifiers, a needle lift transducer and pressure measuring sensors. Using the measuring instruments we measured the needle lift, injection pressures in the nozzle, combustion pressures, fluctuations of pressure in the charge and exhaust ducts in relation to the crankshaft angle,crank revolutions per minute, preinjection angle and engine loading. Moreover, we measured the fuel consumption, the temperature of cylinders and bridges between valves in the engine.