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The rate of air entrainment into the flame and the rate of heat release are thermodynamically calculated in a DI diesel engine: A two-zone model is proposed which uses as input data three measured values of cylinder pressure, flame temperature, and injection rate. The correlations between both rates under various conditions make it clear that the combustion during early and main periods of diffusion combustion is mainly controlled by air entrainment into the flame. The effects of injection pressure, piston configuration, and swirl intensity on the air entrainment are also studied. And the extent of mixing in the flame is evaluated by the equivalence ratio in the flame which is also obtained by the same model. The trends of exhausted NO and soot concentrations well correlate with the equivalence ratios in the flame and measured flame temperatures under all conditions studied.

Control of turbulence during the compression stroke is suggested by both theoretical calculations and experimental results obtained with an LDV measurement in a motored engine. The authors have found experimentally that when an axial distribution of swirl intensity exists, a large-scale annular vortex is formed inside the cylinder during the compression stroke and this vortex generates and transports turbulence energy. A numerical calculation is adopted to elucidate this phenomenon. Then, an axial stratification of swirl intensity is found to generate a large-scale annular vortex during the compression stroke by an interaction between the piston motion and the axial pressure gradient. The initial swirl profile is parametrically varied to assess its effect on the turbulence parameters. Among calculated results, turbulence energy is enhanced strongest when the swirl intensity is highest at the piston top surface and lowest at the bottom surface of the cylinder head.

The OH and soot in an unsteady flame, which was achieved in a rapid compression machine, were visualized simultaneously by the laser-induced fluorescence and laser-induced scattering techniques. The fuel mixture consisting of 90% paraffin hydrocarbon (reference fuel) and 10% polypropylene-glycol was used to reduce the optical attenuation caused by dense soot cloud. The simultaneous images of the fluorescence from OH and scattering from soot show that the soot and OH exist separately from each other in the leading portion of the spray flame, and the OH is formed earlier than the soot in the near field region of spray flame.

The cross-sectional distribution of fuel vapor concentration in an evaporating spray was measured quantitatively by a new scattering imaging technique, silicone particle scattering imaging method, which was proposed in a previous paper[1]. When fuel containing silicone oil injected into a nitrogen environment at high temperature, the volatile base fuel in the droplets vaporized rapidly, leaving behind small droplets of silicone oil suspended in the vapor-gas mixture. The silicone oil droplets were illuminated by a thin laser sheet, and the scattered light was imaged by a CCD camera. The cross-sectional distribution of vapor concentration was estimated from the scattering image of the silicone oil droplets by Mie scattering theory. The results demonstrated clearly the inhomogeneity of the fuel vapor concentration. The distribution of vapor concentration was discontinuous, and islands of rich mixture with a scale of several millimeters existed in the center region of the spray.

A theoretical model for predicting the evaporation process of liquid fuel sprays in both diesel and S.I. stratified charge engines is presented: The injected liquid fuel is assumed to break up into droplets with a certain time delay which is determined through careful experiments on the heat absorption process of injected fuel in a high temperature, high pressure inert atmosphere. The evaporation, heat absorption, and motion of these droplets are computed, together with the change of gas conditions inside the spray, by solving a coupled system of equations made up of heat and mass balance between droplets and gas. The effects of such parameters as the surrounding gas conditions, fuel properties, and spray characteristics on evaporation are investigated by the model. Reference is also made to the application of a predicted result to the calculation of burning rate in a direct injection diesel engine.

The present paper describes the particulate formation in diesel flames considering the flame structure and its similarity to that of gaseous turbulent diffusion flames. A comparison of spatial variations of soot concentration, equivalence ratio and flame temperature between diesel flames and turbulent diffusion flames reveals the facts that soot particles are mostly farmed in a region where the equivalence ratio is near stoichiometric and the flame temperature is the highest in both flames, and that in diesel flames this region exists generally near the flame tip. A close inspection of high speed photographs of diesel flames suggests the three major routes of soot emission from diesel engines: quenching of flamelets detached from the flame tip due to 1) the flame impingement onto the wall; and 2) cooling of the flamelets by the bulk air; and 3) survival of soot containing flamelets inside the flame.

The turbulent dispersion of particles in an unsteady two dimensional particle-laden jet was simulated by a discrete vortex method coupling with a model of gas/particles interaction. Numerical analysis of a spray yielded the distributions of vorticity, fuel mass concentration and local Sauter mean diameter (SMD) of droplets in a spray. The predicted distribution of local SMD of droplets in a spray demonstrated that the size of droplets in the spray periphery is larger than that of droplets in the center region of spray. This trend of distribution of drop size coincided with that of measured one. The predicted distributions of drop size and vorticity revealed that the larger droplets are easily centrifuged to the periphery of the spray. The effects of the pattern of injection rate on the mixing process in a transient spray were also investigated.

Soot concentration is very high in the periphery near the head of an unsteady spray flame which is achieved in a quiescent atmosphere in a rapid compression machine. To reduce soot concentration in this region, it was intended to improve fuel-air mixing by letting the flame impinge on a turbulence-generating plate. Two types of turbulence-generating plates, one donut-type, the other cross-type, were tested. Soot concentration in the flame was imaged using the laser shadow technique. The effect of injection pressure on soot reduction by the flame impingement was also investigated. The overall soot concentration is reduced significantly in the case when the flame impinges on the cross-type turbulence-generating plate at 50 mm (333 nozzle diameters) from the nozzle exit. The flame impingement on the cross-type turbulence-generating plate at 333 nozzle diameters makes soot reduction little dependent on injection pressures.

The accuracy of the injection rate meter based on W. Zeuch's method in the measurement of multiple injection rate and amount was calibrated using a small cam driven piston that is driven by an electric motor. For the pre- or early-injection, a sensor with a high sensitivity can be applied to measure the small pressure increase due to the small injection amount. In case of the multiple injection that has the post and/or late injection, a pressure sensor with a low sensitivity must cover not only the large pressure increase due to the main injection but also the small pressure increase due to the post and/or late injection because the output of the high sensitivity sensor is saturated after the main injection. So the linearity of the low sensitivity pressure sensor was calibrated with the cam driven piston prior to the experiment with the actual injection system.

According to previous papers on the combustion process in LHR diesel engines the combustion seems to deteriorate in LHR diesel engines. However it has been unclear whether this was caused by the high temperature gas or high temperature combustion chamber walls. This study was intended to investigate the effect of gas temperature on the rate of heat release through the heat release analysis and other measurements using a rapid compression-expansion machine. Experiments conducted at high gas temperatures which was achieved by the employment of oxygen-argon-helium mixture made it clear that the combustion at a high gas temperature condition deteriorated actually and this was probably due to the poorer mixing rate because of the increase in gas viscosity at a high gas temperature condition.

Experiments on the effects of temperature T and equivalence ratio ϕ on soot formation at high pressures up to 5 MPa were conducted. The soot formation region is mapped on ϕ-T diagram using the results obtained in the experiments and the published data. NO formation region is also determined by the Zeldovich equations and is plotted on the same diagram. The time histories of ϕ and T of the flame in a DI diesel engine which was obtained by a gas sampling study, are plotted on the ϕ-T diagram to form a trajectory. Discussion of the trajectory in relation to both soot and NO formation region gives suggestion of a possibility of high temperature - rich mixture combustion to reduce particulate formation in diesel engines.

The relation between the characteristics of a non-evaporating spray and those of a corresponding frame achieved in a rapid compression machine was investigated experimentally. The fuel injection pressure was changed in a range of 55 to 260 MPa and the other injection parameters such as orifice diameter and injection duration were changed systematically. The characteristics of the non-evaporating spray such as the Sauter mean diameter and the mean excess air ratio of the spray were measured by an image analysis technique. The time required for a pressure rise due to combustion was taken as an index to characterize the flame. It was concluded that the mean excess air ratio of a spray is the major factor which controls the burning rate and that the high injection pressure is effective in shortening the combustion duration and reducing soot formation.

Local heat flux from the flame to the combustion chamber wall, q̇, was measured the wall surfaces of a rapid compression-expansion machine which can simulate diesel combustion. Temperature of the flame zone, T1, was calculated by a thermodynamic two-zone model using measured values of cylinder pressure and flame volume. A local heat transfer coefficient was proposed which is defined as q̇/(T1-Tw). Experiments showed that the local heat transfer coefficient depends slightly on the temperature difference, T1-Tw, but depends significantly on the velocity of the flame which contacts the wall surface.

The characteristics of diesel spray and flame in a quiescent atmosphere were studied as a function of injection pressure ranging from 30 to 110 MPa. Measurements included the spray form and Sauter mean diameter of a non-evaporating spray, the liquid phase penetration of an evaporating spray and the visualization of sooting zone in a flame. Experimental results show that high pressure injection improves the atomization and air entrainment of non-evaporating spray and that the liquid phase penetration of evaporating spray is hardly affected by injection pressure, demonstrating a promotion of evaporation with injection pressure. Visualization of the sooting zone in a flame made it clear that high pressure injection is advantageous in reducing soot formation and shortening the combustion duration.

A rapid compression-expansion machine was developed, which can simulate intake, compression, expansion and exhaust strokes in a single Diesel cycle by an electrically controlled and hydraulically actuated driving system. The whole system which is composed of a hydraulic actuator, fuel injector and a valve driving device, is sequentially controlled by a micro-computer. The machine features; 1) accurate control of piston position at TDC, 2) no effect of lubricant on HC emission due to the use of dry piston rings; 3) independent control of local wall temperature; and 4) high power output to drive heavy piston at high frequency. The single cycle operation permits Diesel combustion experiments under a wide range of operating conditions and easy access of optical diagnostics with minimized amount of test fuel. The performance test showed that the machine can drive a DI Diesel type piston with a 100 mm bore at a maximum frequency of 16.7 Hz at a maximum compression pressure of 15 MPa.

The filtration efficiency of a DPF drops when it suffers a failure such as melting and cracks during regeneration. And then, on-board diagnostics (OBD) device has become needed worldwide to detect a DPF failure. In the development of an OBD soot sensor, evaluation of the sensor demands a portable instrument which can measure the soot concentration for on-board and in-field use. Some of the emission regulations require the in-field emission measurements under normal in-use operation of a vehicle. This study is intended to develop a high sensitivity and high response portable smoke meter for on-board soot measurements and a reference to OBD soot sensors under development. The smoke meter accommodates a 650 nm laser diode, and its principle is based on light extinction in high soot concentration range and backward light scattering for low soot concentration measurement.

The applicability of several popular diesel particulate matter (PM) measurement techniques to low temperature combustion is examined. The instruments' performance in measuring low levels of PM from advanced diesel combustion is evaluated. Preliminary emissions optimization of a high-speed light-duty diesel engine was performed for two conventional and two advanced low temperature combustion engine cases. A low PM (<0.2 g/kg_fuel) and NOx (<0.07 g/kg_fuel) advanced low temperature combustion (LTC) condition with high levels of exhaust gas recirculation (EGR) and early injection timing was chosen as a baseline. The three other cases were selected by varying engine load, injection timing, injection pressure, and EGR mass fraction. All engine conditions were run with ultra-low sulfur diesel fuel. An extensive characterization of PM from these engine operating conditions is presented.

Some problems associated with applying LDA to the measurement of air motion in the engine’s cylinder are studied experimentally for both the forward and the back scattering technique in a motored diesel engine. The effects of the doppler broadening caused by the velocity gradient and the diameters of the scattering particles are discossed. The decaying process and the structure of the in-cylinder flow field are studied using the measurements of the main flow velocity, the turbulent intensity and macro scales and normalised power spectrum of the turbulence. A comparison measurement is also made between the forward scattering and the back scattering techniques.

A DI diesel engine with an air cell was developed as one of the combustion systems for reducing soot emission from diesel engines: The air is accumulated in the air cell during the compression stroke and is injected into the main chamber during a period after the end of injection. The air jet stirs the stagnant flame and promotes soot oxidation. A comparative experiments with the conventional system made it clear that the air-cell system effectively reduces soot emission at a medium and high load condition.

A thermodynamic two-zone model which assumes a stoichiornetric burned gas region and unburned air region is presented in an attempt to calculate more precise rate of heat release of diesel combustion. A comparison is made of the rate of heat release obtained by the two-zone model with that obtained by the conventional single-zone model. It shows around 10 % increase in the rate of heat release with the two-zone model. The effect of state equation of gas is also examined with the single-zone model and the use of a real gas law in stead of the perfect gas law is found to yield minor difference in the rate of heat release at a high boost operating condition.