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With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole (10 holes) nozzles with different nozzle hole length and hole diameter were investigated in conjunction with a series of computational and experimental methods. Specifically, the Computational Fluid Dynamics (CFD) commercial code was used to predict the internal flow variation inside different nozzle configurations, and the high-speed video observation method was applied to visualize the spray evolution processes under non-evaporating conditions.

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.

Previous research has shown that the reduced nozzle hole diameter and elevated injection pressure are effective for preparing a uniform fuel-air mixture in a direct injection (D.I.) Diesel engine. A micro-hole nozzle with a hole diameter of 0.08 mm and an ultra-high injection pressure of 300 MPa have been employed to investigate the mixture formation process under various conditions. The aim of the current work is to clarify the effect of nozzle hole diameter and injection pressure on flame lift-off and soot formation processes. The free sprays from the micro-hole and conventional nozzles were investigated at a high-temperature, high-pressure constant volume vessel. A high-speed video camera system was employed to record the non-vaporizing sprays and combustion. The direct photography of OH chemiluminescence was used to provide information about the high temperature combustion process and to measure the flame lift-off length.

The fuel-ambient gas interaction process of the free diesel spray injected from the micro-hole nozzle (0.08 mm) into the quiescent and engine-like ambient gas condition was investigated by means of the laser-induced fluorescence - particle image velocimetry (LIF-PIV) technique in non-evaporating condition. Direct photography with high speed video camera and two color pyrometry were applied to analyze the evaporation spray and flame characteristics. Three injection pressures from 100, 200 to 300 MPa and two ambient gas densities of 11 and 15 kg/m₃ were selected as testing conditions. The entrained mass flow rate of the ambient gas through the whole spray boundary, the ratio of the total ambient gas entrainment rate to the fuel injection rate, etc., were calculated by using the ambient gas velocity data obtained by the LIF-PIV technique and used to correlate the combustion behavior.

Spray characteristics are of great importance to achieve fuel economy and low emissions for a D.I. gasoline engine. In this study, the characteristics of the fuel spray as well as its interaction with a cross-flow were investigated. The fuel was injected by a VCO injector into an optically accessible rectangular wind tunnel under the normal temperature and pressure, in which the direction of the injection was perpendicular to the direction of the cross-flow. The velocity of the cross-flow varied from 0 to 10 m/s while the injection pressure was 5 and 10 MPa. With using the high speed video camera and the PIV system, the spray profile, velocity distribution and the penetration distance were measured. The lower penetration distance can be obtained with the lower injection pressure and the increased velocity of the cross-flow, however the injected fuel expands along the direction of the cross-flow, which indicates that spray atomization and mixing of fuel and air are enhanced.

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.

Hydrogen (H2) addition is widely used for natural gas combustion to improve the engine efficiency. However, less attention was paid on the various ignition timings for the maximum brake torque (MBT) and brake thermal efficiency (BTE). In order to check the ignition timing effect, experiments were performed in a spark ignition engine with engine speed fixed on 1500 revolutions per minute (rpm). Firstly, CH4 was only used for combustion with excess air ratio (λ) changing from 0.8 to 1.4. Then, co-combustion of 50 vol% CH4 and 50 vol% CO2 was checked to simulate methane fermentation gas. Finally, H2 was added with volume percentage varying from 5% to 20%. Among these discussions, torque, brake mean effective pressure (BMEP), BTE and cylinder pressure were evaluated. Based on the results, high efficiency can be achieved by advancing the ignition timing with H2 addition at λ=1.4. However, with H2 addition, the ignition timing should be retarded to obtain higher BTE.

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.

A phenomenological spray-combustion model of a D.I. Diesel engine was applied to study the engine parameters with potential for reducing NOx and smoke emissions. The spray-combustion model, first developed at the University of Hiroshima in 1976, has been sophisticated by incorporating new knowledge of diesel combustion. The model was verified using data from an experimental, single cylinder, D.I. diesel engine with a bore of 135mm and a stroke of 130mm. After the verification process, calculations were made under a wide range of the engine parameters, such as intake air temperature, intake air pressure, intake swirl ratio, nozzle hole diameter, injection pressure, air entrainment rate into the spray, and injection rate profile. These calculations estimated the effects of the engine parameters on NOx, smoke and specific fuel consumption. As a result of the calculations, an approach for the low NOx and smoke emission engine was found.

The ignition and flame propagation processes of a propane-air mixture compounded with a kerosene spray were investigated in order to allow a better understanding of the multi-phase combustion process of the spray compound mixture in a direct injection stratified charge (DISC) engine. The ignition probability and the flame propagation velocity, as functions of the overall equivalence ratio, fraction of propane in the fuel, ignition energy and the Sauter mean diameter of the spray, were measured under atmospheric conditions. The development of the flame kernel and the propagating flame were observed by a high-speed video camera combined with a schlieren system. Adding small amounts of the kerosene spray to the lean propane-air mixture improved the ignition probability. However, the ignition probability depended strongly on the Sauter mean diameter and the ignition energy. Replacing the propane with the kerosene spray in a rich propane-air mixture increased the flame propagation velocity.

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.

A new technique was proposed for the simultaneous measurement of the concentration of fuel vapor and liquid in an evaporating diesel spray injected into a high temperature and high pressure environment. This technique was based on the principle of the absorption of ultraviolet laser light by fuel vapor and the scattering of visible laser light by fuel droplets in the diesel spray. For this principle, α-methylnaphthalene was used as a test fuel. Measuring the transmissivity of ultraviolet and visible laser lights absorbed and scattered by β-methylnaphthalene spray made it possible to analyze the fuel vapor concentration, droplets density and the mixture temperature in the diesel spray. A computerized tomographic transfer technique was also adopted to analyze three-dimensional fuel concentration distribution in the spray.

A comprehensive model for sprays emerging from high-pressure 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.

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.

Cross-sectional distributions of the liquid phase temperatures in fuel sprays were measured using a laser-induced fluorescence technique. The liquid fuel (n-hexadecane or squalane) was doped with pyrene(C16H10). The fluorescence intensity ratios of the pyrene monomer and excimer emissions has temperature dependence, and were used to determine the liquid phase temperatures in the fuel sprays. The measurements were performed on two kinds of sprays. One was performed on pre-heated fuel sprays injected into surrounding gas at atmospheric conditions. The other was performed on fuel sprays exposed to hot gas flow. The spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence image by the temperature dependence of the intensity ratio.

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.

The two-dimensional distributions of the liquid phase temperatures in diesel sprays injected into high-pressure and high-temperature environments were measured using the laser-induced fluorescence technique. The liquid fuel (n-hexadecane) was doped with pyrene(C16H10). The fuel spray doped with pyrene was injected under a high-pressure of 3.1MPa and a high-Temperature of 773K. The evaporating diesel spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The fluorescence intensity ratios of the pyrene monomer and excimer emissions have temperature dependence, and were used to determine the liquid phase temperatures in the diesel sprays. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence images by the temperature dependence of the intensity ratio.

In the previous study of the authors, it was found that some benefits for the mixture preparation of DI gasoline engines can be offered by splitting the fuel injection, such as the phenomenon of high density liquid phase fuel piling up at the leading edge of the spray can be circumvented. In a further analysis, the vapor quantity in the “stable operating” range (equivalence ratio of vapor ϕv in a range of 0.7≤ϕv≤1.3) was significantly increased by the split injection compared to the single injection. In this work, the mechanism of the effect of the split injection on the mixture formation process was studied by combining the laser-sheet imaging, LIF-PIV and the LAS (Laser Absorption Scattering) technique. As a result, it is found that the spray-induced ambient air motion can help the formation of the more combustible mixture of the split injection whereas it played a minus role of diluting the spray by the single injection.

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.

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).