Characterization of the Rate of Injection of Diesel Solenoid Injectors Operated in the Multiple Injection Strategy: A Comparison of the Spray Momentum and Bosch Tube Methods

Multiple injection strategies can be used for controlling the heat release rate in an engine, particularly in compression ignition engines. This can mitigate the heat transfer losses and overcome the limitation related to the maximum pressure allowed for a particular engine. Controlling heat release with repetitive injections requires precise characterization of the fuel injection rates. 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. This study investigates the fuel injection behavior of a high-flow-rate solenoid injector operated with single and double injections. Two characterization methods, the momentum flux, and the Bosch tube are used and compared to investigate their suitability with the multiple injection strategies. Experiments with single injection are conducted by varying the Energizing Timing (ET) from 0.5 up to 2 ms. The tests with multiple injections (i.e., double injections) are conducted with a fixed ET of 0.5 ms, while the dwell times (δt) are varied from 0.1 up to 1 ms. All tests are performed at 500, 1000, 1500, and 2000 bar rail pressures. Depending on the injection pressure, the injector’s needle could not fully close with short dwell times and the injections are merged. 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. The effective duration of injection is overpredicted with the Bosch tube method. The momentum flux method is demonstrated to be more suitable for measuring the ROI of multiple injection strategies

Computational investigation of methanol pre-chamber combustion in a heavy-duty engine

This work explored the potential of methanol pre-chamber combustion (PCC) for heavy-duty engine applications. An optical engine experiment was conducted to visualize the jet flame development. The measured pressure traces and natural flame luminosity images were also used for the validation of three-dimensional computational fluid dynamics simulations. It was demonstrated that the main chamber (MC) combustion was successfully established by the reactive jet issued from the pre-chamber. Compared to methane PCC in our previous study, the distributed reacting jets were significantly thinner, in particular at the learner condition. The active PCC mode, which comprises enrichment of the mixture in the pre-chamber (PC) by means of direct methane injection, was effective in improving the engine performance. However, excessive PC fueling ratio (PCFR) resulted in lower thermal efficiency due to the higher wall heat transfer and combustion losses. In addition, the effects of various PC and piston geometries on the methanol/methane PC combustion were evaluated. The combination of an optimized PC and a flat piston yielded the highest thermal efficiency owing to the relatively lower combustion and wall heat transfer losses. At engine loads higher than 12.5 bar indicated mean effective pressure, exhaust gas recirculation must be implemented to avoid end-gas autoignition and reduce nitric oxides (NOx) emissions. As expected, the increase in (CR) further promoted engine work because of the higher expansion ratio. With CR of 13 and 14, higher thermal efficiency and lower NOx emission were simultaneously achieved under both intermediate and high loads when the engine was operating at the pure methanol PC combustion mode

Computational Investigation of the Effects of Injection Strategy and Rail Pressure on Isobaric Combustion in an Optical Compression Ignition Engine

The high-pressure isobaric combustion has been proposed as the most suitable combustion mode for the double compre4ssion expansion engine (DCEE) concept. Previous experimental and simulation studies have demonstrated an improved efficiency compared to the conventional diesel combustion (CDC) engine. In the current study, isobaric combustion was achieved using a single injector with multiple injections. Since this concept involves complex phenomena such as spray to spray interactions, the computational models were extensively validated against the optical engine experiment data, to ensure high-fidelity simulations. The considered optical diagnostic techniques are Mie-scattering, fuel tracer planar laser-induced fluorescence (PLIF), and natural flame luminosity imaging. Overall, a good agreement between the numerical and experimental results was obtained. Upon validation, the optimized models have been used to conduct a comparative study between the conventional diesel combustion (CDC) and the isobaric combustion cases with different pressure levels, in terms of engine performance and emissions. Compared to the CDC case, the isobaric combustion cases led to a lower NOx emission but higher sooting tendency due to the increased diffusion combustion feature, although most of the soot was oxidized in the later engine cycle. To further reduce soot emission, the effects of various rail pressures and injector holes number were evaluated. The results indicated that the higher injection pressure was more effective in soot reduction for the isobaric combustion case but it deteriorated the thermal efficiency. It was also found that increasing the number of injector holes from the reference six to ten led to the lowest soot emission without significantly affecting the efficiency

Comparative Study of Spark-Ignited and Pre-Chamber Hydrogen-Fueled Engine: A Computational Approach

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H2 in internal combustion engines (ICEs) faces three major challenges: high NOx emissions, severe pressure rise rates, and pre-ignition at mid to high loads. In this study, the potential of H2 combustion in a truck-size engine operated in spark ignition (SI) and pre-chamber (PC) mode was investigated. To mitigate the high pressure rise rate with the SI configuration, the effects of three primary parameters on the engine combustion performance and NOx emissions were evaluated, including the compression ratio (CR), the air–fuel ratio, and the spark timing. In the simulations, the severity of the pressure rise was evaluated based on the maximum pressure rise rate (MPRR). Lower compression ratios were assessed as a means to mitigate the auto-ignition while enabling a wider range of engine operation. The study showed that by lowering CR from 16.5:1 to 12.5:1, an indicated thermal efficiency of 47.5% can be achieved at 9.4 bar indicated mean effective pressure (IMEP) conditions. Aiming to restrain the auto-ignition while maintaining good efficiency, growth in λ was examined under different CRs. The simulated data suggested that higher CRs require a higher λ, and due to practical limitations of the boosting system, λ at 4.0 was set as the limit. At a fixed spark timing, using a CR of 13.5 combined with λ at 3.33 resulted in an indicated thermal efficiency of 48.6%. It was found that under such lean conditions, the exhaust losses were high. Thus, advancing the spark time was assessed as a possible solution. The results demonstrated the advantages of advancing the spark time where an indicated thermal efficiency exceeding 50% was achieved while maintaining a very low NOx level. Finally, the optimized case in the SI mode was used to investigate the effect of using the PC. For the current design of the PC, the results indicated that even though the mixture is lean, the flame speed of H2 is sufficiently high to burn the lean charge without using a PC. In addition, the PC design used in the current work induced a high MPRR inside the PC and MC, leading to an increased tendency to engine knock. The operation with PC also increased the heat transfer losses in the MC, leading to lower thermal efficiency compared to the SI mode. Consequently, the PC combustion mode needs further optimizations to be employed in hydrogen engine applications