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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.

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.

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.

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. The dispersion process was, however, computed by solving the conservation equations of the gaseous components and enthalpy by the finite difference technique. The sub-models were combined for predicting the three-dimensional distributions of the gaseous components and the temperature in the combustion chamber, and finally the cylinder pressure, heat release rate, engine performance and pollutant emissions (NO and soot).

Quantitative imaging of the fuel concentration distribution was made in the combustion chamber of a propane-fueled spark ignition (SI) engine with the employment of laser-sheet-induced Rayleigh scattering technique for realizing the 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-micro- channel plate image intensifier. The measurements were done at the crank angle of 270°ATDC in the combustion chamber of the engine motored at 200rpm with an air fuel ratio of 13 for various injection timing, injection direction and intake flow. The results show that with an appropriate matching of fuel injection timing, injection direction and intake flow, a stratified distribution of the fuel concentration can be realized.

Planar laser-induced fluorescence (PLIF) technique was employed to perform the quantitative measurements of the cyclic variation of mixture concentration in the combustion chamber of a spark ignition (SI) engine. Nitrogen dioxide was used as the fluorescence tracer to simulate the fuel vapor. A Nd:YAG laser operated at its second harmonic wavelength was employed as the light source. The original engine was modified to introduce laser sheet light into the combustion chamber and the induced fluorescence was captured by a CCD camera fitted with a gated image intensifier. The measurements were done at the engine crank angles of 180° ∼ 300° ATDC with the engine speeds of 200 ∼ 400 rpm and the injection timings of -70 °, 50° and 100° ATDC. A theoretical analysis was made to describe the cyclically varying characteristics of the mixture concentration.

The fuel injection characteristics of Dimethyl Ether(DME) were calculated and compared with the calculated results of diesel fuel using a simulation model of an in-line diesel injection system in order to clarify the differences between the injection characteristics of the two fuels. Moreover, numerical analyses for the DME injection were performed while changing the fuel parameters and the injection system parameters in order to estimate the effects of these parameters on the fuel injection characteristics. The effects of some of these parameters were evaluated by experimental results conducted in a constant volume vessel. Furthermore, the spray tip penetration was calculated using the computed results of the injection pressure. As a result of this study, the injection characteristics of the DME fuel are basically confirmed. By the macroscopic analyses of these spray characteristics, the DME spray behavior in a combustion chamber can be estimated.

Spray combustion processes of palm oil biodiesel (PO) and conventional diesel fuels were simulated using the CONVERGE CFD code. Thermochemical and reaction kinetic data (115 species and 460 reactions) by Luo et al. (2012) and Lu et al. (2009) (68 species and 283 reactions) were implemented in the CONVERGE CFD to simulate the spray and combustion processes of the two fuels. Tetradecane (C14H30) and n- heptane (C7H16) were used as surrogates for diesel. For the palm biodiesel, the mixture of methyl decanoate (C11H20O2), methyl-9-decenoate (C11H19O2) and n-heptane was used as surrogate. The palm biodiesel surrogates were combined in proportions based on the previous GC-MS results for the five major biodiesel components namely methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate.

In order to investigate effects of the multi-hole nozzle with micro orifices on mixture formation processes in Direct-Injection Diesel engines, mixture characteristics were examined via an ultraviolet-visible laser absorption scattering (LAS) technique under various injectors. The injection quantity per orifice per cycle was reduced by nozzle hole sizes. The LAS technique can provide the quantitative and simultaneous measurements of liquid and vapor phases concentration distributions inside of the fuel spray. Mass of ambient gas entrained into the spray, liquid/ vapor mass and mean equivalence ratio of total fuel were obtained based on Lambert Beer's law. As a result, the leaner and more homogeneous fuel-gas mixture can be achieved by reducing the nozzle hole diameter, in the meanwhile more ambient gas were entrained into the spray. Moreover, relationships between mixture formation and D.I.

A pancake-type constant-volume combustion chamber was used to investigate the combustion and NOx emission characteristics of propane-air and hydrogen-air mixtures under various charge stratification patterns, which were obtained by variations of the initial charge and injected mixture concentrations and the ignition spark timing. A planar laser-induced fluorescence from nitrogen dioxide as gas fuel tracer was applied to measure the mixture distribution in the test chamber. The second harmonic output of pulsed Nd; YAG laser was used as a light source for fluorescence excitation. The fluorescence images were corrected by a gated image-intensified CCD camera. The quantitative analysis of fuel concentration was made possible by the application of linearity between fluorescence intensity and NO2 concentration at low trace level.

Among the alternative fuels, dimethyl ether (DME), one of the oxygenated fuels, attracts attention as an alternative fuel for the Diesel engine since the properties of the DME are fitted to the Diesel engine combustion and the know-how development has been made of the mass production of the DME from a natural gas. In this study, experiments were performed of ignition characteristics of the DME and Diesel fuel sprays injected by a D.I. Diesel injector into a high-pressure, high-temperature vessel. The fuel injection was made by a Bosch type injection system. A schlieren optical system was adopted for visualizing the ignition process as well as the vaporization process of the DME and Diesel fuel sprays. The ignition delay was measured by using a photo-sensor which had a sensitivity in the wavelength range from visible to ultraviolet. Pressure and temperature of the ambient air and the oxygen concentration of the ambient air were changed as experimental parameters.

Experiments and modeling of the fuel spray trajectory and dispersion influenced by both a swirling gas flow and wall impingement were performed under simulated direct injection (D.I.) diesel engine conditions at a high pressure and high temperature. A spray was injected into the steady swirling gas flow and impinged on the simulated piston cavity wall in a constant-volume bomb. High-speed Schlieren photographs provided the informative data on the behavior of the spray vaporizing in such diesel-like circumstances. A simplified computational model was developed to describe the spray trajectory and the fuel vapor dispersion in the D.I. diesel combustion chamber. The model includes the effects of the breakup on the trajectory and the vaporization of the spray, and the effects of the swirling gas flow and the wall impingement on the dispersion of the fuel vapor.

Ethanol is regarded as the promising alternative fuel for gasoline to meet the strict low emission standard for spark ignition engines. In this study, the spray mixture formation process for different ethanol blended fuels, including E0 (gasoline), E85 (85% volume of ethanol and 15% volume of gasoline) and E100 (ethanol), has been evaluated using hole-type nozzle by the measurement of Laser Absorption Scattering (LAS) technique in a constant volume vessel. Based on the principle of LAS, the quantitative vapor and liquid phase distribution from different ethanol blended fuel can be obtained by the light extinction regime. Aiming to analyze the effect of mixture formation and evaporation for different components of blended fuel or pure gasoline and ethanol, the vapor distribution of gasoline was determined by using p-xylene, which had similar physical properties to gasoline, especially higher boiling temperature components, and higher absorption for ultraviolet.

This paper studies the ignition processes of two biodiesel from two different feedstock sources, namely waste cooked oil (WCO) and palm oil (PO). They were investigated using the direct photography through high-speed video observations and detailed chemical kinetics. The detailed chemical kinetics modeling was carried out to complement data acquired using the high-speed video observations. For the high-speed video observations, an image intensifier combined with OH* filter connected to a high-speed video camera was used to obtain OH* chemiluminscence image near 313 nm. The OH* images were used to obtain the experimental ignition delay of the biodiesel fuels. For the high-speed video observations, experiments were done at an injection pressure of 100, 200 and 300 MPa using a 0.16 mm injector nozzle.

An experimental study was conducted to investigate the flame propagation characteristics in the presence of a heterogeneous concentration distribution of a fuel-air mixture in order to provide fundamental knowledge of the effects of gaseous mixture concentration heterogeneity on the combustion process. Different propane-air mixture distributions were produced by the reciprocating movements of a pair of perforated plates in a constant volume combustion chamber. The mean equivalence ratio of the fuel-air mixture was varied from 0.7 on the lean side to 1.6 on the rich side, the turbulence intensity in the combustion chamber was also varied at levels of 0.185 m/s, 0.130 m/s, 0.100 m/s, and 0.0 m/s. By an independent control of the mixture distribution and the turbulence intensity in the combustion chamber, the flame structure and flame propagation speed at various heterogeneous levels of the mixture distribution were investigated in detail.