No abstract

As a miniaturized direct-injection (DI) solution, a self-pressurized injector is of great significance for small aviation piston engines, such as the spark-ignited two-stroke heavy-fuel engines. Accurate control of the timing and amount of injections is an important application prerequisite. In this paper, a high-speed camera is employed to study the spray characteristics, injection delay and fuel injection duration under three drive modes in a constant-volume bomb environment. The results show that the 8-A constantcurrent drive mode ensures the minimum injection dead zone and linearity of the flow characteristic curve, and the spray characteristics are close to those under a peak current of 10 A and holding current of the 8-A drive mode, which indicates that the drive circuit can be simplified. Ambient pressure increase leads to an increased injection delay and shortened injection duration. Therefore, it is recommended to apply the 10-A constant-current drive mode to reduce the impact of the ambient pressure. The double-injection characteristics of the self-pressurized injector are also studied, and the results demonstrate that when the interval time is reduced to 2 ms, the spray characteristics of the secondary injection are affected, and when the interval time is reduced to 0.2 ms, the spray characteristics of the primary injection are also affected. To ensure consistency of the spray characteristics, the minimum spray interval should be longer than 3 ms. INDEX TERMS aviation aircraft, direct injection, spray characteristics, piston engine, self-pressurized injector.

The application of direct injection (DI) technology can effectively improve the atomization effect of heavy fuel to reduce the fuel loss of heavy fuel engines (HFE). The fuel spray characteristics directly affect the combustion performance of the engine. To investigate the atomization process and evaporation characteristics of heavy fuel in-cylinder for an air-assisted direct injection (AADI) engine, a simulation calculation model of AADI HFE was established with the use of a computational fluid dynamics tool. The air-assisted injector model and the one-dimensional performance calculation model were verified by test data. The influences of injection timing and injection pressure on the spray characteristics and mixture formation in the engine cylinder were discussed. The results show that the mixture concentration distribution is uniform after the injection timing is advanced, and the mass fraction of the fuel evaporation increases. The earlier injection timing can provide the fuel with sufficient time to evaporate, while the later injection timing will result in increasing the Sauter mean diameter (SMD) of the fuel droplets, and the unevaporated heavy fuel in the combustion chamber tends to become concentrated. With the increase in air injection pressure, the distribution of the mixed gas in the cylinder becomes uniform, and the SMD of the fuel droplets in the cylinder decreases. When the injection pressure is 0.65 MPa and 0.75 MPa, the difference between the SMD of the fuel droplets in-cylinder decreases, and a favorable fuel atomization effect can be maintained.

To study the influence of control parameters under cold-start and low-load conditions on the performance of a heavy-oil, two-stroke, direct-injection, ignition engine for use in aviation, the operation of a two-stroke, direct-injection engine was studied in a bench test. The results were as follows: ① When the ambient temperature is 15 °C, the battery voltage is 12.4 V, and the peak speed of the starting motor is 1200 r/min. As the concentration factor increases, the cold-start speed increases, and the fuel consumption increases. The influence on the cold start is reduced after reaching a certain concentration. The cold-start time decreases with the increasing magnetization pulse width. The cold-start time is the shortest at an oil–gas interval of 6 ms. ② Under small-load conditions of 3000 r/min and 14% to 16% throttle, a higher ignition energy increases the engine power. Pollutant emissions are the lowest when the fuel injection is 7.5 mg and the excess air coefficient is approximately 1.1.