Keiya Nishida

Simplified Three-Dimensional Modeling of Mixture Formation and Combustion in a D.I. Diesel Engine

This paper describes a simplified three-dimensional modeling of the mixture formation and combustion processes in a direct injection (D.I.) diesel engine. The fuel-air mixing and combustion processes in the D.I. diesel engine can be characterized by the combined effects of some processes, such as spray trajectory, fuel vaporization, gas motion, combustion, and dispersion of gaseous components and enthalpy. Each process was computed by a simple sub-model based on the experimental results and empirical equations. Reasonable agreement between computed and experimental results for these engine variables demonstrate that, with appropriate adjustments to the empirical coefficients of each model, the model produces qualitatively realistic predictions of the in-cylinder processes and engine performance. (A) For the covering abstract see IRRD 865952.

Imaging of droplets and vapor distributions in a Diesel fuel spray by means of a laser absorption–scattering technique

The droplets and vapor distributions in a fuel spray were imaged by a dual-wavelength laser absorption-scattering technique. 1,3-dimethylnaphthalene, which has physical properties similar to those of Diesel fuel, strongly absorbs the ultraviolet light near the fourth harmonic (266 nm) of a Nd:YAG laser but is nearly transparent to the visible light near the second harmonic (532 nm) of a Nd:YAG laser. Therefore, droplets and vapor distributions in a Diesel spray can be visualized by an imaging system that uses a Nd:YAG laser as the incident light and 1,3-dimethylnaphthalene as the test fuel. For a quantitative application consideration, the absorption coefficients of dimethylnapthalene vapor at different temperatures and pressures were examined with an optical spectrometer. The findings of this study suggest that this imaging technique has great promise for simultaneously obtaining quantitative information of droplet density and vapor concentration in Diesel fuel spray.

Fuel Spray Simulation of High-Pressure Swirl-Injector for DISI Engines and Comparison with Laser Diagnostic Measurements

A comprehensive model for sprays emerging from highpressure swirl injectors in DISI engines has been developed accounting for both primary and secondary atomization. The model considers the transient behavior of the pre-spray and the steady-state behavior of the main spray. The pre-spray modeling is based on an empirical solid cone approach with varying cone angle. The main spray modeling is based on the Liquid Instability Sheet Atomization (LISA) approach, which is extended here to include the effects of swirl. Mie Scattering, LIF, PIV and Laser Droplet Size Analyzer techniques have been used to produce a set of experimental data for model validation. Both qualitative comparisons of the evolution of the spray structure, as well as quantitative comparisons of spray tip penetration and droplet sizes have been made. It is concluded that the model compares favorably with data under atmospheric conditions. However, discrepancies occur under higher ambient pressures, suggesting that the physics of the breakup mechanism should be further investigated for these conditions.

Effect of flat-wall impingement on diesel spray combustion:

The effect of spray–flat-wall interaction on the diesel combustion characteristics in a constant-volume vessel was investigated. A flat wall was fixed perpendicular to the nozzle hole axis. Three injection pressures of 100 MPa, 150 MPa and 200 MPa and a single nozzle hole with a diameter of 0.133 mm were employed. Mie scattering was adopted to detect the spray formation process; OH* chemiluminescence and natural colour luminosity were conducted to analyse the combustion process. The two-colour method was applied to calculate the soot emissions and the temperature distribution. The results reveal that, in comparison with a free spray flame, flat-wall impingement causes diesel combustion to deteriorate when the liquid phase–wall interaction occurs; however, when an appropriate impinging distance (longer than liquid-phase penetration) is selected, combustion is observed to be enhanced. As for the impinging spray flame, when the injection pressure is increased, soot formation decreases; however, combustion is not linearly enhanced by increasing the injection pressure, and the OH* chemiluminescence intensity achieves the highest value with an injection pressure of 150 MPa.

An investigation of mixture formation and in-cylinder combustion processes in direct injection diesel engines using group-hole nozzles:

Abstract Mixture properties of the transient fuel spray injected by group-hole nozzles were quantitatively studied in a constant volume chamber via the laser absorption scattering (LAS) technique, and compared with conventional single-hole nozzles. Specific areas investigated included non-evaporating and evaporating ambient conditions, and the conditions of free spray and spray impinging on a flat wall. The particular emphasis was on the effect of one of the key parameters of the group-hole nozzle structure, namely, the interval between orifices. Subsequently, in-cylinder ignition and combustion processes were investigated by direct flame visualization in a single-cylinder optical research engine using the group-hole nozzle and the standard multi-hole nozzle, together with heat release analysis. Results show that the group-hole nozzle can produce a smaller Sauter mean diameter (SMD) of droplets under the non-evaporating condition. Under the evaporating condition, for the free spray cases, there exists a trade-off between the fuel evaporation and the spray penetration in the application of the group-hole nozzle. With the increase in interval between orifices, the ratio of evaporation increases, but the spray tip penetration decreases. For the spray impinging on a flat wall, the group-hole nozzle can enhance the spray tip penetrations to some extent compared with the single-hole nozzles. Flame images taken in a direct injection optical engine show that the enhancement of the fuel atomization and evaporation by the group-hole nozzle may contribute to a decrease in overall flame luminosity level, suggesting reduced soot formation in diesel engines.

Characteristics of the ignition and combustion of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine

Abstract The effect of injection pressures at 100 MPa and 200 MPa respectively on the ignition and combustion characteristics of biodiesel fuel spray injected by a common-rail injection system for a direct-injection diesel engine was investigated. Two biodiesel fuels (namely biodiesel fuel from palm oil (BDFp) and biodiesel fuel from cooking oil (BDFc)) and JIS#2 diesel fuel were utilized in this research. The Mie scattering technique was used to characterize both the non-evaporating and the evaporating spray formation processes. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. Two-colour pyrometry was applied for the soot formation processes. At all injection pressures, the biodiesel fuels (especially BDFp) gave a longer spray tip penetration and a smaller spray angle under the non-evaporating conditions while the liquid-phase penetration length was longer for the biodiesel fuels than for diesel under the evaporating conditions. From estimation using a simplified model for air entrainment by the sprays, the BDFp and BDFc exhibited lower mass ratios of air to fuel than diesel did. The ignition delay was longest for the BDFc while it was shortest for the BDFp. Both the experimental and the predicted flame lift-off lengths for the BDFp were the shortest, indicating the least percentage of entrained stoichiometric air upstream. There was no significant difference between the integrated and averaged KL factors at 100 MPa injection pressure for the BDFc and diesel fuels. At 200 MPa, the BDFc presented much lower integrated and averaged KL factors than diesel did. The averaged flame temperatures of the BDFc were found to be lower than that of diesel. The oxygen content in the BDFc played a significant role in the soot formation in comparison with the oxygen from the percentage of stoichiometric air entrained upstream of the lift-off length.

Effect of Injection Pressure on Ignition, Flame Development and Soot Formation Processes of Biodiesel Fuel Spray

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures. The BDFp’s higher cetane number facilitated shortest ignition delay when compared to the other fuels under all injection pressures. For all the fuels, the lift-off length increased as the injection pressure increased. The percentage of the stoichiometric air entrained upstream of the lift-off length by the BDFp was the lowest. The integrated, average natural luminosities and flame areas of the BDFp and BDFc were smaller at increasing pressures as compared to that of the diesel fuel flames. At the 100MPa injection pressure, the two color pyrometry measurements indicated that there was no significant difference in the integrated and averaged KL factors for all the fuels. At 200 and 300MPa injection pressures, the BDFp and the BDFc presented much lower integrated and averaged KL factors than diesel. The averaged flame temperatures of the BDFp and the BDFc were found to be lower than that of diesel except at the 300MPa injection pressure. The oxygen contents in the BDFp and the BDFc fuels played a significant role on the soot formation process.

Fuel Spray Trajectory and Dispersion in a D.I. Diesel Combustion Chamber

The trajectory and dispersion of a fuel spray vapourising in a combustion chamber are of importance in the mixture formation and combustion of a direct injection (DI) diesel engine. The paper describes experiments and modelling of the spray, of both swirling gas flow and wall impingement, under simulated conditions. A simplified computational model was developed to describe the spray trajectory and vapour dispersion in the DI diesel combustion chamber. The model includes the effects of the breakup on the trajectory, vapourization, gas flow and dispersion of the fuel vapour. For the covering abstract see IRRD 865952.

Three-Dimensional Spray Distributions in a Direct Injection Diesel Engine

Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditons (pressure and density) at an ambient temperature. The diesel fuel was delivered from a Bosch-type injection pump to a single-hole nozzle, the hole being drilled in the same direction as the original five-hole nozzle. The fuel was injected into a high-pressure bomb in which an engine combustion chamber, composed of a piston, a cylinder head and a cylinder liner, was installed. Distributions of the spray impinging on the simulated combustion chamber were observed from various directions while changing some of the experimental parameters, such as combustion chamber shape, nozzle projection and top-clearance. High-speed photography was used in the constant volume bomb to examine the effect of these parameters on the spray distributions. The spray distributions obtained in the simulated combustion chamber are compared to the distributions calculated by a spray model based on a multi-package, spray model 3 refs., 13 figs., 1 tab.

Vapor/Liquid Behaviors in Split-Injection D.I. Diesel Sprays in a 2-D Model Combustion Chamber

Some experimental investigations have shown that the trade-off curve of NOx vs. particulate of a D.I. diesel engine with split-injection strategies can be shifted closer to the origin than those with a single-pulse injection, thus reducing both particulate and NOx emissions significantly. It is clear that the injection mass ratios and the dwell(s) between injection pulses have significant effects on the combustion and emissions formation processes in the D.I. diesel engine. However, how and why these parameters significantly affect the engine performances remains unexplained. The effects of both injection mass ratios and dwell between injections on vapor/liquid distributions in the split-injection diesel sprays impinging on a flat wall have been examined in our previous work. In this paper, the behaviors of the split-injection diesel sprays in a 2-dimensional model combustion chamber, which was installed in a high-temperature and high-pressure constant volume vessel filled with nitrogen, was observed by use of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique. The effect of the injection mass ratios and the effect of the dwell(s) between injections on the distributions of fuel vapor and droplets were clarified through qualitative imaging of the optical thickness of vapor and the optical thickness of droplets, respectively. The findings give an implication to the potential relation between the vapor/liquid behaviors in the split-injection sprays and the reduction mechanism of NOx and particulate emissions of the D.I. diesel engine.