![]() In conventional diesel combustion, the soot formation at the spray tip with a single injection was diminished with split injection as this induced an improved fuel-air mixing ( Nehmer and Reitz, 1994).Īt high ambient density conditions, we have investigated the potential of employing multiple injections to achieve isobaric combustion using a heavy-duty D13 Volvo engine ( Babayev et al., 2019). Marginal soot levels were observed depending on the adapted injection strategy as the main combustion was more tilted toward the injection at which combustion was phased. It was then shown that NOx emissions with a split injection schematic could be decreased because of the controllability of the rate of heat release (fuel staging) at which the main combustion started. The multiple injection concept was explored to decouple the NOx-soot trade-off, for instance, in the work of Nehmer and Reitz (1994), when operated at high injection pressure with split injections. This development facilitates controlling the fuel flow rate to shape the rate of heat release, which subsequently can improve engine efficiency and reduce emissions ( Mohan et al., 2013 Lam et al., 2015 Cung et al., 2017 Bhavani Shankar et al., 2017 Lam et al., 2019 Al Ramadan et al., 2020 Harsh et al., 2020 Tang et al., 2020 Jin et al., 2021 Aljabri et al., 2022 Zhang et al., 2022). The state-of-the-art direct injection systems allow a large degree of flexibility to operate at ultra-high injection pressures and multiple repetitive injection pulses. With ultra-high-pressure injection systems and precise control of fuel injection, the engine-out emissions, such as soot, unburned hydrocarbons, carbon monoxide, and oxides of nitrogen ( N O x ), were reduced to comply with stringent regulations. The substantial advancement in injection systems in the past decade has significantly contributed to improving the efficiency of compression ignition engines. The momentum flux method is demonstrated to be more suitable for measuring the ROI of multiple injection strategies. The effective duration of injection is overpredicted with the Bosch tube method. The momentum flux method has faster ramp-up and decaying and more oscillations in the quasi-steady-state phase compared to the Bosch tube method. Depending on the injection pressure, the injector’s needle could not fully close with short dwell times and the injections are merged. All tests are performed at 500, 1000, 1500, and 2000 bar rail pressures. The tests with multiple injections (i.e., double injections) are conducted with a fixed ET of 0.5 ms, while the dwell times ( δ t ) are varied from 0.1 up to 1 ms. ![]() Experiments with single injection are conducted by varying the Energizing Timing (ET) from 0.5 up to 2 ms. ![]() Two characterization methods, the momentum flux, and the Bosch tube are used and compared to investigate their suitability with the multiple injection strategies. This study investigates the fuel injection behavior of a high-flow-rate solenoid injector operated with single and double injections. In such a configuration, the injector used should be characterized for its hydraulic delay, rate of injection, and the effect of dwell timing with multiple injections. ![]() Controlling heat release with repetitive injections requires precise characterization of the fuel injection rates. This can mitigate the heat transfer losses and overcome the limitation related to the maximum pressure allowed for a particular engine. Multiple injection strategies can be used for controlling the heat release rate in an engine, particularly in compression ignition engines.
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