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The fuel economy of recent small size DI diesel engines has become more and more efficient. However, heat loss is still one of the major factors contributing to a substantial amount of energy loss in engines. In order to a full understanding of the heat loss mechanism from combustion gas to cylinder wall, the effect of hole size and rail pressure at similar injection rate condition on transient heat flux to the wall were investigated. Using a constant volume vessel with a fixed impingement wall, the study measured the surface heat flux of the wall at the locations of spray flame impingement using three thin-film thermocouple heat-flux sensors. The results showed that the transferred heat was similar under similar injection rate profiles. However, in case of flame luminosity, temperature distribution, characteristic of local heat flux and soot distribution was also similar except the smaller nozzle hole size with higher injection pressure.

Simplified visualization of the fuel spray developing process in a small D.I. diesel engine was made by the liquid injection technique. In this technique, a liquid fuel was injected into another liquid to simulate injection into a high pressure gaseous atmosphere. For obtaining spray characteristics in the liquid similar to a diesel spray in a high-pressure gaseous atmosphere, the similarity principles based on the Reynolds number of the fuel flow at a nozzle hole and empirical equations of the spray penetration including the breakup length were introduced in this study. Especially, the injector was newly designed for the liquid injection technique based on these similarity principles. The behavior of the spray in a swirling flow was investigated. The spray with different breakup length shows different behavior in the same swirling flow.

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.

An experimental study was made of the two-dimensional distributions of the fuel vapor concentration simulated by Freon-12 in the combustion chamber of a SI engine. Laser Rayleigh scattering was applied for this remote, nonintrusive and highly space- and time-resolved measurement. The original engine was modified to introduce YAG laser-induced sheet light into the combustion chamber and the scattered light was captured by a CCD camera fitted with a gated double-microchannel plate image intensifier. The results showed that the fuel vapor concentration was highly heterogeneous during the intake stroke and the inhomogeneity decreased in the compression stroke. But, even at the end of the compression stroke, a number of small lumps of inhomogeneous mixture still existed randomly in the engine combustion chamber, which is assumed to cause the heterogeneity of the mixture strength field at the spark discharge.

An experimental study on emission formation processes, such as these of nitric oxide, particulate and total hydrocarbon in a small direct injection (D.I.) diesel engine was carried out by using a newly developed total in-cylinder sampling technique. The sampling method consisted of rapidly opening a blowdown valve attached to the bottom of the piston bowl, and quickly transferring most of the in-cylinder contents into a large sampling chamber below the piston. No modification of the intake and exhaust ports in a cylinder head was required for the installation of the blowdown apparatus. The sampling experiment gave a history of spatially-averaged emission concentrations in the cylinder. The effects of several engine variables, such as the length-to-diameter ratio of the nozzle hole, the ratio of the piston bowl diameter to the cylinder bore and the intake swirl ratio, on the emission formation processes were investigated.

This paper describes information of the swirling flow in a direct-injection diesel engine which has over-head valves and a troidal cavity. The forward-scattering laser doppler velocimeter was used. The “SIDE VIEW” optical arrangement was adopted in the engine to measure the flow in the cylinder and in the cavity with little modification on the configuration of the combustion chamber. The properties of the swirling flow were discussed for three kinds of cylinder heads which produced different intake flows. As a result, the relationship between the mean velocity, the turbulence and the cycle-to-cycle variation was revealed. Further, the variation of the flow pattern and the swirl intensity was indicated as a function of the crank angle and the axial distance.

Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditions (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 impinged 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.

Three-Dimensional visualization technique based on volume rendering method has been developed in order to translate a calculated result of diesel combustion simulation into an realistically spray and flame image. This paper presents an overview of diesel combustion model which has been developed at Hiroshima University, a description of the three-dimensional visualization technique, and some examples of spray and flame image generated by this visualization technique.

A simple, but useful method is described for predicting the swirl speed during the compression process in a direct injection diesel engine. The method is based on the idea of dividing the combustion chamber into two volumetric regions and computing the variation of the angular momentum in each region. Laser doppler velocimeter measurements in a motored engine proved the validity of the idea that the volume in the combustion chamber should be treated as two regions, that is, the cylindrical volume inside the piston-cavity radius, and the annular volume outside the piston-cavity radius. Distributions of tangential velocities were measured for different conditions, including the intake port configuration, the piston cavity shape, the compression ratio and the engine speed. These results were integrated in the two regions and provided the measured “two volume-regions” swirl ratio. At the same time, the computation was carried out for the same experimental conditions.

In this study, formation behaviors of soot in laminar diffusion flames of diesel fuel with fatty acid or fatty acid methyl ester (FAME) were investigated. Oleic acid and oleic acid methyl ester were selected as fatty acid and fatty acid methyl ester. Combustion gas emitted from the laminar diffusion flame was sampled, and PM composition in the gas was analyzed. Laser induced incandescence (LII) and laser induced fluorescence (LIF) techniques were applied to measure soot and polycyclic aromatic hydrocarbon (PAH) distributions in the laminar diffusion flames. As the results, soot emission and soot incandescence distributions were decreased by the addition of fatty acid or fatty acid methyl ester. Moreover, PAH concentration in the closed flame became high by addition of fatty acid or fatty acid methyl ester.

The main component of PM (particulate matter) formed in the combustion field is soot. Soot is formed by pyrolysis, polymerization and partial oxidation of hydrocarbon fuel. In this experimental research, the effects of temperature and oxygen on PAHs (polycyclic aromatic hydrocarbons) and PM formed from benzene-oxygen mixture were investigated by independent control of temperature (Tf = 1,073 K, 1,173 K, 1,273 K, and 1,338 K) and oxygen concentration (ϕ = ∞, 6.2, and 2.8). In order to investigate the growth processes of PAHs, mass concentrations of naphthalene, biphenyl, phenanthrene, anthracene, and pyrene were measured. As the result, it was found that mass concentration of biphenyl (two-ring PAH, nC = 12) was higher than naphthalene (two-ring PAH, nC = 10) under benzene-N2 mixture condition (without oxygen condition:ϕ = ∞). Mass concentrations of biphenyl and naphthalene were almost same levels under ϕ = 6.2 condition.

The objective of this paper is to summarize experimental results which were previously reported by the authors and to derive many useful empirical equations concerning the diesel fuel sprays. The empirical equations for break-up length, spray angle, spray tip penetration and drop size distribution of the diesel sprays are introduced to discuss the internal structure of the spray. According to the effect of injection pressure and ambient pressure on the break-up length and drop size of the diesel spray, the spray structure can be divided into two categories; incomplete and complete sprays. The equations which express the break-up length and mean diameter of the incomplete and complete sprays were obtained using different techniques according for the dominance of one or more break-up mechanisms.

In a direct injection diesel engine, fuel spray was auto-ignited by an elevated temperature and pressure atmosphere in a combustion chamber. Since an ignition might appear in which a suitable mixture for exothermic reaction was prepared and flame might be developing to a combustible mixture, a settlement of ignition in time and space could control the entire combustion. The ignition position was usually investigated with photometric observations such as high-speed video systems. However plane observations could not inform the exact position of the ignition because spray had the 3D structure. In this paper, a new trial for the measurement of the ignition position was reported. A single shot diesel spray injected into a test chamber was ignited by elevated temperature and pressure atmosphere in the chamber. The chamber had an impingement plate so as to measure an ignition delay of a wall impingement diesel spray.

In a direct injection diesel engine, liquid fuel was injected through a multi-hole injection nozzle to a combustion cavity. The spray impingement on the cavity wall made the quick mixing of sprayed fuel and air. Then the spray impingement process was considered as the key process of the mixture formation, and this process was widely investigated. Since the cavity had too small space for free movement of plural sprays injected by a multi-hole injection nozzle, sprays after impingement were interacted together on the cavity wall. This movement was generally recognized but the detail behavior was not yet clarified. In this study, single shot diesel spray injected into a high-pressure test vessel, in which the impingement plate was mounted, was used to investigate the above movement.

The injection amount per stage in a multiple injection strategy is smaller than a conventional single-stage injection. In this paper, the effect of the injection amount (0.27mg, 0.89mg, 2.97mg) under 100MPa injection pressure and the effect of injection pressure (100MPa, 150MPa, 170MPa) under different injection amounts (0.27mg, 2.97mg) on the spray and mixture formation characteristics were studied by analyzing the vapor/liquid phase concentration distributions obtained under various conditions via using the tracer LAS technique. The spray was injected into a high-pressure and high-temperature constant volume vessel by using a single-hole nozzle with a diameter 0.133mm. The higher the injection pressure with a smaller injection amount is, the shorter the spray tip penetration and leaner air-fuel mixture occur. The combustion processes had been examined by a high-speed video camera with the two-color pyrometry method.

An experimental and numerical study was conducted on the spray and mixture properties of a hole-type injector for direct injection (D. I.) gasoline engines. The Laser Absorption Scattering (LAS) technique was adopted to simultaneously measure the spatial concentration distributions and the mass of the liquid and vapor phases in the fuel spray injected into a high-pressure and high-temperature constant volume vessel. The experimental results were compared to the numerical calculation results using three-dimensional CFD and the multi-objective optimization. In the numerical simulation, the design variable of the spray model was optimized by choosing spray tip penetration, and mass of liquid and vapor phases as objective functions.

Different ethanol-gasoline blended fuels, namely the E0 (100% gasoline), E85 (85% ethanol and 15% gasoline mixed in volume basis) and E100 (100% ethanol) were injected by a valve-covered-orifice (VCO) hole-type nozzle in a condition simulating the near top dead center (TDC). Two typical injection pressures of 10 and 20MPa were adopted to clarify the spray and flame behaviors. The correlation of the upstream unburned fuel and the flame propagation was analyzed by the high-speed imaging of shadowgraph. Moreover, the effects of ignition timing and location on the flame propagation were discussed based on the imaging of OH* chemiluminescence.

Experimental and computational studies were carried out to characterize the spray development and evaporation processes of multi-hole injector for direct injection spark ignition (DISI) engines. The main injector parameter to be investigated in this study is a diverging angle between neighboring two holes. In the experimental study, the influence of the diverging angle on evaporation process of fuel spray from two-hole injector was investigated using Laser Absorption Scattering (LAS) measurement. Smaller diverging angle causes larger spray tip penetration because the momentum of the spray from one hole emphasizes another, when two spray merge to one. Moreover, spray tip penetration decreases at certain diverging angle due to the negative pressure region between two sprays. Mechanisms behind the above spray behaviors were discussed using the detailed information on the spray and ambient gas flow fields obtained by the three dimensional computational fluid dynamics (CFD).

Reduction of orifice diameter of nozzle is advantageous to the fuel atomization in a D.I. diesel engine. However, the diameter reduction is usually accompanied with decrease of spray tip penetration, thus worsening fuel spatial-distribution and fuel-air mixing. In this paper, a group-hole nozzle concept was proposed to solve the problem resulting from minimization of orifice diameter. Compared to the conventional multi-hole nozzle, group-hole nozzle has a series group of orifices, and each group consists of two micro-orifices with a small spatial interval and small angle. For examining the characteristics of the spray injected by the group-hole nozzle, the ultraviolet-visible laser absorption-scattering (LAS) imaging technique was adopted to determine vapor concentration and droplets density as well as other spray characteristics such as spray angle and penetration of both vapor and liquid phases.

The objectives of this study are to investigate the effects of premixed charge compression ignition (PCCI) strategies with split injection on soot emission characteristics. The split injection conditions included three injection intervals (1.1 ms, 1.3 ms, and 1.5 ms) and three injection quantity fraction ratios (Q1/Q2 = 10.0/14.6 mm3/st, 15.2/9.4 mm3/st, and 20.0/4.6 mm3/st). The results in real engine tests showed that shorter injection intervals, and the 1st injection quantity contributes to reduced soot emissions. A rig test with high-pressure and high-temperature constant-volume vessel (CVV) and a two-dimensional (2D) model piston cavity were used to determine correlations between injection conditions and soot emissions. During the rig test, fuel was injected into the CVV by a single-hole nozzle under split injection strategies. The injection strategies include the same injection intervals and quantity fraction ratios as in the real engine test.