Abstract
An experimental study was performed to explore the influence of dwell time on the hydraulic interactions between injection events using pilot injection strategy, split injection strategy, post injection strategy and a solenoid diesel injector. To do so, a sweep of dwell time from 0.55 up to 2 ms using all multiple injection strategies and levels of rail pressure, of 80, 100 and 120 MPa, and single level of back pressure, of 5 MPa, was performed. The hydraulic interactions between injection events were characterized through the second injection hydraulic delay and second injection mass in an injection discharge curve indicator equipped with all the components required for its operation and control. In order to define the operating conditions of the multiple injection strategies, to ensure the same injected fuel mass in all cases, the characteristic curves of injection rate for the solenoid diesel injector studied were obtained. The second injection hydraulic delay increases with dwell time values in the range of 0.55–0.9 ms for all multiple injection strategies and levels of rail pressure tested. Conversely, the second injection hydraulic delay decreases with dwell time values higher than 0.9 ms. Moreover, the second hydraulic delay depends mainly on the dwell time and not on the injected fuel mass during the first injection event. The second injection mass increases with dwell values less than 0.6 ms. By contrast, the second injection mass is not significantly affected by that of the first injection at a dwell time higher than 0.6 ms.
Highlights
NOx and soot emissions are the main pollutants from diesel engine, which are regulated by emissions standards [1,2,3]
Similarity, How et al [15] investigated the effects of biodiesel blends, fuel injection timing and split injection schemes on the engine performance, emissions and combustion characteristics of a medium-duty diesel engine, and concluded that multiple split injections is a practical strategy to simultaneously decrease the NOx and smoke emission when the start of injection timing is fine-tuned and is an ideal alternative to operate with biodiesel fuel
If the attention is focused on the prail level of 80 MPa, the second injection hydraulic delay values are 0.26 ms and 0.43 ms for dwell time of 0.55 ms and 0.9 ms, respectively, when utilizing the pilot injection strategy
Summary
NOx and soot emissions are the main pollutants from diesel engine, which are regulated by emissions standards [1,2,3]. Ambrosio et al [13], studied different injection strategies on the performance and emissions of a low compression ratio Euro 5 diesel engine operated with high EGR rates. They found that the experiment design of optimized triple and quadruple injection strategies led to improved soot-NOx trade-offs, with respect to the pilot and main injection strategy calibration. Mie et al [16], investigated the influence of two pilot injections on combustion and emissions using a single-cylinder turbocharged diesel engine They observed that by adjusting the fuel quantity in both pilot injections, it is possible to reduce the NOx and soot emissions. Liang et al [17], analysed the mixing process and its influence on the combustion and emission characteristics under the pilot injection strategy and utilizing a low-speed two-stroke diesel engine, and they found that, adjusting the pilot injection’s time, it is possible to reduce part of the NOx emissions
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