Temporal Evolution of Split-Injected Fuel Spray at Elevated Chamber Pressures

Abstract

For reducing soot and NOx emissions, an effective method is to apply split injection strategies. In this research, characteristics of split injection were investigated by applying the pilot-main injection strategy and main-post injection strategy. The injection mass of fuel with the two strategies was measured by an in-house fuel injection rate test system based on the Bosch method. The development of spray tip and tail penetrations, as well as the evolvement of the spray angle when applying these two injection strategies, were explored by employing the high speed shadowgraphy at various injection pressures and surrounding gas densities. The results indicate the tail penetration rate of spray has no relation to the fuel injection pressure. However, the increased injection pressure causes a faster penetration development in the spray tip position. It was also found that the spray tip penetration rate of the second spray is slightly slower than that of the first spray at the beginning stage of injection, but it was significantly larger than the first one at the later stage.

Analysis of the Influence of Diesel Spray Injection on the Ignition and Soot Formation in Multiple Injection Strategy

“…In single injections, the start of combustion (SOC) can be identified by the high rate of heat release and the increase in chamber pressure present during the premixed combustion of the second stage, which, from the optical point of view is visualized as a sudden radial expansion [31]. This is valid for the first pulse in multiple injections, nonetheless, this pulse creates local conditions that could promote a faster SOC for the second injection [32] and the radial expansion would be very small [3] or non-existent, as is seen in Figure 5. Besides, once the thermal radiation from soot appeared in the frames, the intensity levels of these pixels resembled the background, creating problems in contour depiction.…”

Recent Research Progress on Black Carbon Emissions from Marine Diesel Engines

“…According to Shundoh et al [172], it was found that combination of pre-injection and high-pressure injection in a high-speed engine leads to a significant reduction in NOx and smoke emissions by 35% and 60-80%, respectively. The main injection is split several times to improve the mixture formation process [173] and prevent the formation of BC. As shown in Figure 13, splitting the main injection or post injection can prevent the accumulation of excessively rich fuel and promote the accelerated oxidation of the high-concentration BC particles in the spray head.…”

Numerical study of different shape design of piston bowl for diesel engine combustion in a light duty single-cylinder engine

“…Figure 11 shows the results of spray angle evolvements when applying injection strategy under the same injection pressure, and density of the fuel conditions had shown with only different cylinder combustion chamber geometry. The reason for the large spray angle in the initial injection phase because that the fuel was injected into a relatively stationary air environment and the air at the nozzle outlet was squeezed and pushed into the radial direction however, the spray angle remains nearly stable during the later injection stage ( Taşkiran and Ergeneman, 2011 ; Payri et al., 2017 ; Wu et al., 2019 ). This can be attributed to the increased momentum exchange at higher surrounding gas densities as the fuel droplets are more closely surrounded by environmental gases.…”