Search Results

The time of, and location where ignition first occurs in a diesel fuel spray were investigated in a rapid compression machine (RCM) using the two–dimensional techniques of silicone oil particle scattering imaging (SSI), and the planar laser induced fluorescence (LIF) of formaldehyde. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the LIF images of the formaldehyde formed in a diesel fuel spray during ignition process have been successfully obtained for the first time by exciting formaldehyde with the 3rd harmonic of the Nd:YAG laser. SSI images of the vaporizing spray, and the LIF images of formaldehyde were obtained together with the corresponding time record of combustion chamber pressures at initial ambient temperatures ranging from 580 K to 790 K.

CNG/diesel dual-fuel engine is using CNG as a main fuel, and injects diesel only a little as an ignition priming. In this study, remodeling an existing diesel engine into dual-fuel engine that can inject diesel with high pressure by CRDI (Common Rail Direct Injection), and injecting CNG at intake port for premixing. The results show that CNG/diesel dual-fuel engine satisfied coordinate torque and power with conventional diesel engine. And CNG alternation rate is over 89% in all operating ranges of CNG/diesel dual-fuel engine. PM emission is lower 94% than diesel engine, but NOx emission is higher than diesel engine. The output of dual fuel mode is 95% by the diesel mode. At this time, amount of CO₂ and PM are decreased while CO, NOx, and THC are increased. In NEDC mode, exhaust gases except NOx are decreased.

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.

Super lean burn technology is conceived as one of methods for improving the thermal efficiency of SI engines[1][2]. For lean burn, reduction of heat loss and the due to decrease in flame temperature can be expected. However, as the premixed gas dilutes, the combustion speed decreases, so the combustion fluctuation between cycles increases. Also, to improve the thermal efficiency, the ignition timing is advanced to advance the combustion phase. However, when the combustion phase is excessively advanced, knocking occurs, which hinders the improvement of thermal efficiency. Knocking is a phenomenon in which unburned gas in a combustion chamber compressed by a piston and combustion gas suffer compression auto-ignition. It is necessary to avoid knocking because the amplitude of the large pressure wave may cause noise and damage to the engine. Also, knocking is not a steady phenomenon but a phenomenon that fluctuates from cycle to cycle.

An on-board measurement system that simultaneously measures road traffic, vehicle running conditions and exhaust emissions was installed in a diesel freight vehicle with two tons payload. Actual NOx mass emissions were compared with that measured in a typical test mode for urban cities on a chassis dynamometer. The frequency of vehicle accelerations in actual urban cities was found to exceed that of a typical test mode for urban cities on a chassis dynamometer, which resulted in increased NOx from actual running conditions compared with the typical test mode for urban cities. The dynamics of NOx emissions at an actual roadside was also analyzed. It was observed that NOx emission based on distance with an actual city route test was about two times higher than that of a free way route and a typical test mode for urban cities. The reason for high NOx with the city route was explained by the higher frequency of lower gears at which higher NOx is emitted.

Reduction of particulate emissions from diesel engine is an important theme from the view point of air pollution. Experiments were carried out using a four-stroke single cylinder direct-injection diesel engine. A new method to measure diesel particulates has been developed. Particulates were sampled with a freezing method just behind an exhaust valve and examined through a scanning electron microscope. Shape and structure of particulates and the size distributions are measured under wide operating conditions obtained with above method. The total mass of particulate emissions was measured using a dilution tunnel sampling system. The heat release processes were analyzed using indicator diagrams and the relation between burning condition and particulate emissions were discussed, after systematic experiments under constant revolution speed of 2000 r/min for several load and injection timing conditions.

In the HCCI (Homogeneous Charge Compression Ignition) engine, a mixture of fuel and air is supplied to the cylinder and auto-ignition occurs resulting from compression. This method can expand the lean flammability limit, realizing smokeless combustion and also having the potential for realizing low NOx and high efficiency. The optimal ignition timing is necessary in order to keep high thermal efficiency. The Ignition in the HCCI engine largely depends on the chemical reaction between the fuel and the oxidizer. Physical methods in conventional engines cannot control it, so a chemical method is demanded. Combustion duration is maintained properly to avoid knocking. In addition, the amount of HC and CO emissions must be reduced. The objective of this study is to clarify the following through calculations with detailed chemical reactions and through experiment with the 2-stroke HCCI engine: the chemical reaction mechanism, and HC and CO emission mechanisms.

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.

A simulation study was conducted to examine the transition from SI combustion to HCCI combustion in a two-stroke free piston engine fuelled with propane. Operation of the free piston engine was simulated based on the combination of three mathematical models including a dynamic model, a linear alternator model and a thermodynamic model. The dynamic model included an analysis of the piston motion, based on Newton's second law. The linear alternator model included an analysis of electromagnetic force, which was considered to be a resistance force for the piston motion. The thermodynamic model was used to analysis thermodynamic processes in the engine cycle, including scavenging, compression, combustion, and expansion processes. Therein, the scavenging process was assumed to be a perfect process. These mathematical models were combined and solved by a program written in Fortran.

The rate of heat release of a free diesel flame was measured with a rapid compression machine which has a compression ratio of 14.7 and a combustion chamber with a diameter of 196 mm and a thickness of 40 mm. Basing on the experimental observations of the high speed photographs of the spray and flame, the authors proposed a phenomenological model for predicting the rate of heat release of the flame. The model consists of three basic models; air entrainment, mixing and combustion model. It was confirmed that the model could successively simulate the rate of heat release of a diesel flame in the quiescent chamber of the rapid compression machine.

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 new method to determine simultaneously the temperature and the fuel vapor concentration inside an evaporating spray was described by using a laser-induced fluorescence technique. A TMPD doped base fuel composed of C12H26: 22%, C13H28: 54% and C14H30: 30% was injected into the combustion chamber of a rapid compression machine which is filled with a high temperature and high pressure nitrogen. The laser sheet was used for incident light, which was reflected by a prism located inside the combustion chamber and propagated through the center of an evaporating spray. The laser induced fluorescence intensity was imaged by a high speed-gated intensifier from a direction perpendicular to the incident light. The results shows that mixtures with high equivalence ratio are observed in the central region, while low equivalence ratio mixtures are observed in the periphery of the spray. It is also observed that the temperature of richest mixture is 50 K as low as the surrounding gas temperature.

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.

Some conceptual image of a diesel spray flame and its combustion promotion is shown based on the various interpretations of the enormous data obtained in our laboratory in these several years, on the flame temperature measurement by the two color method, the composition analysis by gas sampling, as well as the focus shadow photography, back illuminated photography and luminous photography by a high speed camera, on the diesel spray flame created in a large scale Rapid Compression Machine (diameter ϕ 200 mm thickness 40 mm) and a D-I engine (diameter (ϕ 95 mm)

Air-entrainment characteristics of non-evaporating sprays and flames were measured by means of high-speed photography including ordinary shadowgraphy of sprays, back diffused light illumination photography and laser shadow photography of flames. Effects of injection pressure and nozzle orifice diameter on air-entrainment characteristics were investigated parametrically. The amount of air entrained into a flame was calculated by a two-zone thermodynamic model with data obtained from the photographs and the pressure measurement in the combustion chamber. The air-entrainment characteristics of flames were compared with those of the corresponding sprays. It showed that immediately after the start of ignition, the air entrainment into a flame increased more rapidly as compared with the corresponding spray and then, with the development of diffusion combustion, the air entrainment gradually approached that of the spray.

To understand further the mixing process between the injected fuel and air in the combustion chamber of a diesel engine, the turbulent mixing process in a one-phase, two-dimensional transient jet was theoretically studied using the discrete vortex simulation. First, the simulation model was evaluated by comparisons between calculated and experimental data on two-dimensional turbulent jets. Second, the trajectories of the injected fluid elements marked with different colors were graphically demonstrated. Also the process of entrainment of the surrounding fluid into the jet was visually presented using colored tracers.

In PCCI combustion with multiple injections, the mechanism having two heat release peaks which has a favorable characteristic of reducing noise is studied using numerical tool of single- and also multi-zone model of CHEMKIN PRO. In the present investigation, the physical issues, such as variations in the equivalent ratio and temperature caused by the fuel injection are simplified first so that the key issues of chemical reaction occurred in the combustion chamber can be extracted and are discussed in detail. The results show that the interval of two heat-release peaks can be controlled and as the number of zones of the calculation increases, the change in the timing of a heat release peak is increased but over three-zones, it is not affected any more. This indicates that to study about complex diesel combustion phenomena, three-to four-zone model shall give sufficiently accurate results.

The combustion mechanism of the homogeneous charge compression ignition (HCCI) engine has been investigated by numerical calculations. Calculations were carried out using n-butane/air elementary reactions at 0 dimension and adiabatic condition to simplify the understanding of chemical reaction mechanisms in the HCCI engine without complexities of walls, crevices, and mixture inhomogeneities. n-Butane is the fuel with the smallest carbon number in the alkane family that shows two-stage auto-ignition, heat release with low temperature reaction (LTR) and high temperature reaction (HTR), similar to higher hydrocarbons such as gasoline at HCCI combustion. The CHEMKIN II code, SENKIN and kojima's n-butane elementary reaction scheme were used for the calculations. This paper consists of three main topics. First, the heat release mechanisms of the HCCI engine were investigated. The results show that heat release with LTR is HCHO oxidation reactions.

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.