Effect of injection timing on gasoline homogeneous charge compression ignition particulate emissions

Abstract

Particulate emissions from homogeneous charge compression ignition (HCCI) engines are often considered as negligible and the measurement of particulate matter (PM) with HCCI combustion systems has been rare. An earlier publication in the literature and the authors' own recently published work suggest that PM emissions from gasoline direct injection (DI) HCCI engines should not be neglected. It has been shown that PM emissions from HCCI engines, although generally lower, can be similar to spark ignition (SI) levels for certain engine conditions, especially in the accumulation mode. The present work shows that although injection timing is effective for control of HCCI, it can have a significant impact on PM emissions. Engine speed also appears to have an impact on PM emissions for the HCCI combustion mode. Typically for HCCI operating at 1500 r/min, the total mass and total number of the PM emissions could be up to six times higher when the fuel is injected during the recompression period compared with the case for injection during the inlet valve open period. Similarly, when the engine was operated in SI mode, an attempt to inject fuel close to induction top dead centre (TDC) made the PM emission noticeably higher, reaching unacceptable levels. The split injection strategy for HCCI mode has been investigated for its effect on PM emissions. It has been found that the PM number concentration for split injection lies between the maximum concentration measured for very early injections (near TDC at recompression) and the minimum concentration measured for the latest injections used (at crank angles near to the inlet valve maximum opening time), with the magnitude of number density varying approximately from 0.2 to 1.2 million/cm3. It is also observed that for split injection the number of particulates in nucleation mode varies less, while the number in accumulation mode level varies within a limit of one order of magnitude; both are dependent on the injection strategy. The shape of the PM distribution is such that the nucleation mode exceeds the number concentration of 1×107 (d N d log Dp) and the accumulation mode falls parabolically to approximately 1×106. For comparison, it can be said that the PM number concentration measured in the authors' engine is approximately one order of magnitude lower in accumulation mode than the level for a typical modern diesel engine.

Experimental Investigations of Particulate Size and Number Distribution in an Ethanol and Methanol Fueled HCCI Engine

“…It is reported for a hydrogen (SI) engine that with increasing in-cylinder temperature, organic carbon levels of the PM also increase [36]. This density was also used for PM studies on a gasoline fueled HCCI engine [28]. Similar phenomenon may also be taking place in HCCI combustion engines, and upon increasing the intake air temperature, the rate of pressure rise increases rapidly.…”

“…Findings of numerous medical investigations indicate that several health effects are associated with ultrafine particles having diameters below 100 nm, which are typically emitted during the combustion of fossil fuels. Parameters such as the air/fuel ratio, fuel injection timing, and engine load can increase PM emissions by as much as three orders of magnitude as compared to those for a stoichiometric operation in gasoline engines [20][21][22], In HCCI engine, PM or smoke emissions are frequently reported as "near zero" or "ultralow" [24], However, recent stud ies revealed that although the total PM mass is indeed low, signifi cant numbers of these particles remain in the size range below lOOnm mobility diameter [25][26][27][28][29][30], The study conducted for inves tigation of port fuel injection timing on methanol fueled HCCI combustion showed that particle number emissions are dependent on fuel injection timings and found that start of injection during closed intake valve condition have lower peak concentration of particles [7]. Therefore, measurement and control of engine PM emissions is absolutely necessary.…”

Particulate Morphology and Toxicity of an Alcohol Fuelled HCCI Engine

“…Misztal et al conducted more detailed study of HCCI particle size distributions using DI-HCCI system by injecting unleaded gasoline directly into the cylinder employing negative valve overlap (NVO) to capture residuals [26]. Other investigation by Misztal et al examined the role of injection timing in PM formation in the same engine [27]. The DI mode of fuel delivery led to discovery of high sensitivity of PM formation to injection timings.…”

Effect of Start of Injection on the Particulate Emission from Methanol Fuelled HCCI Engine

“…With HCCI combustion, emissions of PM, or smoke, are frequently described as "near zero" or "ultra-low" [12]. However recent investigations have shown that although the total mass of PM is indeed low, significant numbers of particles remain in the size ranges below 100 nm mobility diameter [13][14][15][16][17]. This size range is well within the measurement capabilities of modern nano-particle instrumentation, which is well suited for studies in HCCI particle emissions.…”

“…Misztal et al conducted more detailed study of HCCI particle size distributions using DI-HCCI system by injecting unleaded gasoline directly into the cylinder employing negative valve overlap (NVO) to capture residuals [15]. Other investigation by Misztal et al examined the role of injection timing in PM formation in the same engine [16]. The DI mode of fuel delivery led to discovery of high sensitivity of PM formation to injection timings.…”