Influence of Early Fuel Injection Timings on Premixing and Combustion in a Diesel Engine

Abstract

The influence of fuel injection timing on precombustion mixing of diesel fuel and air, combustion, and emissions at early-injection conditions similar to homogeneous charge compression−ignition (HCCI) engine conditions was investigated experimentally in an automotive-size compression−ignition engine and a constant-volume vessel. The injection timing was controlled by electronic fuel injection equipment. In-cylinder pressure measurements, engine-out emission measurements, and imaging of the spray development were used to analyze the ignition delay period and fuel distribution. The ignition delay period was measured over a wide range of injection timings as well as at various compression ratios and engine speeds. With advancing fuel injection timing, the ignition delay increased and the engine-out nitrogen oxides (NO x ) decreased, suggesting that increased premixing time results in a lean mixture and low flame temperature. It was also found that the ignition delay period to decrease NO x emissions to a negligible level was almost the same under any compression ratio or engine speed. From the emissions measurements, a drastic decrease in smoke, hydrocarbon (HC), and carbon monoxide (CO) emissions was observed at specific early-injection timing. To clarify the source of the observed behavior, the diesel spray impinging on the surface of a combustion chamber was visualized in a constant-volume vessel simulating in-cylinder environments under early-injection conditions. The images show that diesel spray should target the bowl-lip area to enhance precombustion mixing, which would be desirable for reducing incomplete combustion products.

Experimental investigation on spray-wall impingement characteristics of n-butanol/diesel blended fuels

“…In order to realize HCCI and PCCI combustion, the early injection has been utilized widely to prolong the fuel/air mixing duration [1][2][3][4]. However, because of the lower gas temperature and density at the early injection timing, some fuel spray unavoidably impinges with the cylinder wall or piston head and causes ''wall-wetting" problem [5][6][7].…”

Guidelines for Improving Diesel Engine Characteristics

“…These spray characteristics play an important role in the efforts to improve engine performance and to reduce fuel consumption and harmful emissions. This is especially true for the fuel atomization (Kook et al 2008).…”

Experimental Investigation on Effect of Wall Roughness and Lubricant Film on the Adhered Fuel Film of N-Butanol-Diesel Blends after Spray Impingement

“…Part of the injected fuel will impact the cylinder liner or piston head. The adhered fuel film evaporates slowly and dilutes the lubricant film on the cylinder liner [4,5]. The mixture concentration near the wall will be too rich, which contributes to a deterioration in combustion and carbon monoxide (CO) and hydrocarbon (HC) emissions.…”