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As a miniaturized direct injection (DI) solution, the pump injector is of great significance for small aviation piston engines, such as two-stroke heavy-fuel engines. The accurate control of the timing and amount of injections is an important application prerequisite. In this paper, the flow characteristics of a pump injector with different driving circuits and parameters are investigated. The effects of the power supply and freewheeling circuits on the opening and closing delays are theoretically studied. A schematic of a self-designed logic control circuit is proposed, and it achieves peak and hold current control without software intervention. Simulations and experiments are carried out, and the drive current and flow characteristics in different states are measured. The results show that when driving a solenoid with a high internal resistance of 2.70 , a single power supply is more suitable, and the variable-freewheeling circuit exhibits excellent performance in terms of control accuracy and energy recovery. Notably, the invariable-freewheeling circuit results in nonlinear flow characteristics, and the nonlinear segment corresponds to the drive current transitioning from the peak value to the hold value. In contrast, the variable-freewheeling circuit overcomes this problem. To comprehensively consider solenoid opening and closing delays, energy consumption and the linearity of the flow characteristics during injection, a peak current of 10 A and a hold current of 8 A are adopted. INDEX TERMS Aviation aircrafts, direct injection, flow characteristics, peak and hold drive, piston engine, pump injector.

The combustion performance of a compression ignition (CI) four-stroke aviation engine fueled with pure No. 3 rocket propellant (RP-3) was experimentally investigated for comparison with diesel. Pilot injection and main injection for RP-3 and diesel were unified under same test conditions. The results show that when burning RP-3, the maximum power of engine is 1% lower than that of burning diesel, with lower specific fuel consumption (SFC) and effective thermal efficiency (ETE). The combustion durations of RP-3 and diesel show small differences of less than 0.4°CA under heavy loads, while the combustion duration of RP-3 is shorter than that of diesel under low loads. The crank angle at 50% mass fraction burnt (CA50) of RP-3 shows differences of 0.3-1°CA compared to that of diesel. For pilot injection at a high engine speed, the ignition delay angle (IDA) of RP-3 is basically equal to that of diesel. With decreasing engine speed, the maximum difference of 1.2°CA in IDAs exist under medium or small loads. For the main injection, the IDA of RP-3 is lager than diesel under heavy loads at various engine speeds. As the load decreases, the IDA of RP-3 is extended. The peak heat release rate (HRR) of RP-3 during main injection combustion is basically the same as diesel under heavy loads, while the intervention effect of unburnt pilot-injected RP-3 under low loads results in a higher peak HRR.

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Purpose The purpose of this paper is to investigate power performance, economy and hydrocarbons (HC)/carbon monoxide (CO) emissions of diesel fuel on a two-stoke direct injection (DI) spark ignition (SI) engine. Design/methodology/approach Experimental study was carried out on a two-stroke SI diesel-fuelled engine with air-assisted direct injection, whose power performance and HC/CO emissions characteristics under low-load conditions were analysed according to the effects of ignition energy, ignition advance angle (IAA), injection timing angle and excess-air-ratio. Findings The results indicate that, for the throttle position of 10%, a large IAA with adequate ignition energy effectively increases the power and decrease the HC emission. The optimal injection timing angle for power and fuel consumption is 60° crank angle (CA) before top dead centre (BTDC). Lean mixture improves the power performance with the HC/CO emissions greatly reduced. At the throttle position of 20%, the optimal IAA is 30°CA BTDC. The adequate ignition energy slightly improves the power output and greatly decreases HC/CO emissions. Advancing the injection timing improves the power and fuel consumption but should not exceed the exhaust port closing timing in case of scavenging losses. Burning stoichiometric mixture achieves maximum power, whereas burning lean mixture obviously reduces the fuel consumption and the HC/CO emissions. Practical implications Gasoline has a low flash point, a high-saturated vapour pressure and relatively high volatility, and it is a potential hazard near a naked flame at room temperature, which can create significant security risks for its storage, transport and use. The authors adopt a low volatility diesel fuel for all vehicles and equipment to minimise the number of different devices using various fuels and improve the potential military application safety. Originality/value Under low-load conditions, the two stroke port-injected SI engine performance of burning heavy fuels including diesel or kerosene was shown to be worse than those of gasoline. The authors have tried to use the DI method to improve the performance of the diesel-fuelled engine in starting and low-load conditions.