Investigations of closely coupled pilot and main injections as a means to reduce combustion noise in a small-bore direct injection Diesel engine

Abstract

Various pilot-main injection strategies are investigated in a single-cylinder optical Diesel engine. It is observed that as the dwell between a single pilot and the main injection is decreased toward zero, combustion noise passes through a minimum, and a reduction of 3 dB is possible. The injection schedules employed in the engine are analyzed with a hydraulic injection analyzer to provide rate shapes for each of the dwells tested. Two distinct injection events are observed even at the shortest dwell tested, and various rate shaping effects are observed with the main injection event as the dwell is adjusted. High-speed elastic scattering imaging of liquid fuel is performed in the engine to examine initial spray penetration rates. These compare favorably to the measured rates of injection, thus providing evidence that rate shaping of the initial phase of the main injection occurs in the engine and that this rate shaping is consistent with the injection rate data. However, experimental evidence suggests that these changes are not responsible for the observed trend in combustion noise as dwell changes. The combination of thermodynamic data and rate of injection data supports the theory that the main injection interacts with the pilot mixture field and influences its heat release process, thus playing a role in decreasing combustion noise. The relative phasing of the pilot and main heat release may play a significant role in reducing combustion noise; further studies will focus on combustion phasing effects.

Exploitation of injection fusion strategies in diesel engines equipped with solenoid injectors

“…In the present case, it is even shown that the application of a single main rate-shaped injection (mM strategy), obtained by means of injection fusion, can also give a better result than a pM injection schedule. Furthermore, the CN results plotted in Figure 10 are also in line with data on digital rate shaping injection schedules tested at moderate loads in Busch et al: 13 the minimum CN was achieved at DT = 140 ms and a reduction of 1.5 dB was detected compared to long DTs.…”

Implementation of Common Rail Direct Injection System and Optimization of Fuel Injector Parameters in an Experimental Single-Cylinder Diesel Engine

“…The combustion process has been smoothened with the association of pilot injection in double-and triple-injection strategies. Introduction of pilot injection reduced the maximum PPR and help in reducing the engine noise [34]. Apart from that, the HHR peak for double and triple injection also reduced as compared to single injection.…”

“…Multiple fuel injection strategies have been proven to reduce the CI engine emission [32,33]. Essentially, introduction of pilot injection can help to reduce the engine noise and NO x emissions [34]. Main injection with fully open needle (rectangular shape) or boost-type shape will also reduce NO x emissions and post injection reduce the soot emissions [35,36].…”

Computational assessment of combustion noise of automotive compression-ignited engines

“…In positive displacement devices such as reciprocating internal combustion engines however, the interplay between thermal and acoustical phenomena is completely different due to their cyclic, unsteady operation, and to the fact that the process occurs in a closed fluid domain. Thus, even being merely direct, combustion noise can be generated by distinct causes within the same combustion process [36,37]. Moreover, the acoustic response can be different owing to the interference between the pressure waves and the chamber walls [38].…”