Spray-wall interactions in direct-injection engines: An introductory overview

Low compression ratio (LCR) approach in diesel engines can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously owing to lower temperatures and longer fuel-air premixing time. The present work investigates the effects of lowering the geometric compression ratio (CR) from 18:1 to 14:1 in a naturally aspirated (NA) single cylinder common rail direct injection (CRDI) diesel engine. Based on the investigations done across the entire speed and load range, significant benefits were observed in the NOx and soot emissions. However, lowering the compression ratio had adverse effects on brake specific fuel consumption (BSFC), unburned hydrocarbon (HC) and carbon monoxide (CO) emissions, especially at low-load and high-speed operating points. To overcome these limitations, novel strategies including split-cooling system (SCS) and secondary exhaust valve opening (SEVO) are proposed in the present work. While the fuel injection parameters optimization specific to LCR could help to improve the BSFC, HC and CO emissions penalty to a reasonable extent, the SCS concept can provide further benefits by reducing the heat loss to coolant and improving the engine component temperatures. Increasing the residual gas fraction using the optimized SEVO concept could further improve the charge temperature leading to a further reduction in the BSFC, HC and CO emissions. The net benefits of the optimized LCR approach are quantified for the modified Indian drive cycle (MIDC) using a one-dimensional simulation tool. The results obtained show a signification reduction of 22% and 74% in NOx and soot emissions respectively as compared to the base 18 CR engine results. Moreover, the penalty in HC and CO emissions could be contained to a large extent resulting in only a slight penalty of 23% and 20% respectively. Furthermore, the higher BSFC with the LCR approach could be successfully addressed and the final values were found to be better than the stock compression ratio by 1.5%. Overall, the strategies proposed in the present work are found to be beneficial to develop modern diesel engines in compliance with the future emission regulations which demand extreme control on NOx and soot emissions.

Section: Introductionmentioning

confidence: 97%

Novel strategies to overcome the limitations of a low compression ratio light duty diesel engine

Vikraman

Anand

Ramesh

2020

“…Spray/wall impingement is an important phenomenon in internal combustion engines and will affect the local fuel-air mixture distribution and the subsequent combustion performance. 1 Interactions of fuel sprays and piston surfaces can be prevalent in direct-injection diesel and gasoline engines. 2,3 The impact of fuel drops on wet walls occurs when the surface is covered with a liquid film resulting from the impact of preceding drops.…”

Section: Introductionmentioning

confidence: 99%

“…The film thickness will affect not only the splash threshold but also the crown formation and evolution, in addition to the properties of the secondary droplets ejected from the rim of the crown. 9,10 Many experimental studies have been intended to develop the splash threshold as a function of the film thickness and proper nondimensional parameters of the incident drop, as shown in equation (1). [11][12][13][14][15] Each study has a specific range of conditions and applications; nonetheless, a clear threshold between deposition and splash was identified.…”

Section: Introductionmentioning

confidence: 99%

“…It is commonly assumed that the wall film stays on and moves with the piston surface. As a result, the relative velocity between the incident drop and the piston surface is used to evaluate the non-dimensional parameters in equation (1). If the velocity of the wall film is available, the relative velocity between the incident drop and the film can be used to evaluate these non-parameters.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of fuel drop impact on wall films using SPH simulation

Pan

Yang

Kong

et al. 2021

The ability to accurately predict the outcome of the drop/wall interaction is essential to engine spray combustion modeling. In this paper, the process of fuel drop impact on a wet wall was simulated using a numerical method based on smoothed particle hydrodynamics (SPH). The present numerical method was first validated using experimental data on the crown height and crown diameter resulting from water drop impact on a liquid film. Then, the impact process of iso-octane drops on wet walls under engine relevant conditions were studied. The presence of a wall film will affect not only the splash threshold but also the crown evolution and the secondary droplets ejected from the rim of the crown. Numerical results show that the splash threshold increases with the film thickness; the splashed mass ratio increases as the kinetic energy of the incident drop increases. The effect of film thickness on the splashed mass ratio is determined by two competing mechanisms. On the one hand, as the film thickness increases, more incident energy will be absorbed and transferred into the crown, thus producing more secondary droplets. On the other hand, more impinging energy will be dissipated during the spreading as the film thickness increases, thus generating fewer secondary droplets. The properties of the secondary droplets are very different as the film thickness increases. Instead of moving outward, the secondary droplets will move upward and even congregate to the center when the film becomes thicker. The impact angle will affect not only the distributions of the secondary droplets but also the splashed mass. The locations and velocities of the secondary droplets were analyzed. These outcomes were incorporated into formulas that can be further developed into a model for simulating engine spray/wall interactions.

“…[2][3][4][5][6][7][8] Spray dynamics from various injector types affects the near nozzle atomization, penetration, cone angle, and air/ fuel mixing in the combustion chamber, which are the key factors governing the quality of combustion and the pollutant formation. [9][10][11][12][13][14] The movement of the needle valve within the injector is determined by the imbalance of forces acting on it. In the nominal design, the axis of the needle valve movement and the needle valve body coincide, so the valve moves concentrically.…”

Section: Introductionmentioning

confidence: 99%

An analytical model of diesel injector’s needle valve eccentric motion

Wang

Moro

Jin

et al. 2021

Past experimental studies have shown that the needle valve of high-pressure diesel injectors undergoes lateral movement and deformation, while the continuous increase in injection pressure enlarges the gap of the needle valve assembly. Two different analytical models, considering or omitting this change are presented here, linking the geometries of the needle valve assembly with the magnitude of needle valve tip lateral movement. It is found that the physical dimensions of the needle valve assembly and the injection pressure have a significant impact on the radial displacement of the needle. For example, for nominal clearances between the needle guidance and the needle valve of about 1–3 μm, the magnitude of the radial movement of the needle tip could reach tens of microns. The model that takes into account the variation of the gap between the needle guide and needle valve is found to give predictions closer to the experimental results.