Analysis of Pilot Injection Effects on Combustion Noise in PPCI Diesel Engines

Abstract

With the common-rail fuel injection systems widely used in diesel engines, the pilot injection strategy has been paid more attention for suppressing pollutants emissions and combustion noise. Using pilot injection strategies, leaner and more homogenous mixture formed in pilot spray results in the combustion process partially fulfill Premixed Charge Compression Ignition (PCCI). Therefore the combustion process of diesel engines with pilot injection strategy can be considered as partial PCCI (PPCI). Pilot injection causes the in-cylinder temperature increase before main injection, which shortens the ignition delay of main spray and consequently reduces the combustion noise, so that the pilot injection has potential to extend PPCI combustion model to high load operation. However, the mechanism of pilot injection effects on the combustion noise has not been fully understood, consequently it is difficult to estimate the lower combustion noise among different pilot injection conditions, that results in difficult selection of the pilot injection parameters in proper way. Thus, in this study, experiments were performed on a single-cylinder DI-diesel engine with pilot and main injection under high load operating conditions. The synthesized in-cylinder pressure levels (CPLs) in different frequency ranges as a novel method were proposed to analyze the pilot injection effects on combustion noise. The results reveal that pilot spray combustion mainly influences the high frequency combustion noise, and the later pilot injection timing causes the higher combustion noise. In the case of the short dwell between pilot and main injection, the increasing pilot injection quantity enhances the high frequency combustion noise. Meanwhile because of the pilot injection quantity increase, decrease of main injection quantity leads to lower combustion noise in middle frequency range.

Assessment of in-cylinder pressure in diesel engines using novel combustion indices

“…Huang et al (Huang et al, 2011) used in-cylinder pressure data to develop combustion indices. Liu et al (Liu et al, 2016) concluded that short dwell between pilot and main injection and increasing pilot injection quantity enhances the high-frequency combustion noise. Vellaiyan et al (Vellaiyan et al, 2018) analyzed the combustion, performance, and emission characteristics of water-emulsified soybean biodiesel fueled diesel engine with alumina nano additive.…”

Mechanism of Combustion Noise Influenced by Pilot Injection in PPCI Diesel Engines

“…Payri et al proposed a novel combustion noise assessment method on the basis of in-cylinder pressure spectrum decomposition [14,21,22]. Besides, cylinder pressure levels (CPLs) have been widely used in combustion noise analysis [13,19,23,24], and in our previous work, CPLs was synthesized in several frequency segments to investigate the effects of pilot injection on combustion noise [25]. Unfortunately, the CPLs or synthesized CPLs can reveal the overall noise level only in the frequency domain, and the lack of time-domain information limits combustion noise analysis.…”