Here in the 21^<st> century, there exist many environmental and natural resource problems such as global warming, fossil fuels resources, and air pollution in urban areas that must be addressed by the automobile industry. The internal combustion engine and electric motor hybrid and fuel cell hybrid vehicles are thought as influential candidates for next generation vehicles to challenge these issues. This paper describes the evolution of ICE vehicles by applying hybrid technology and reports the current status and issues of the ICE hybrid vehicles in the market. With the achievements of this technology that means in combination of advanced ICE and electric drive technologies, I would like to discuss the future potential of ICE vehicles that allow to continue to play an important role in the future.

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Tightening regulations for NO_X emission from diesel engines have revived the significance of temperature measurement of their combustion process. In this study, a newly introduced CMOS camera (HG-100K) was tested to evaluate its potential for combustion visualization and temperature measurement using two-color analysis. Although small modifications in analyzing procedures and some limitations on temperature resolution should be pointed out, measurement results showed its strong potential as a high-speed visualization device for engine combustion. Furthermore, to demonstrate the effectiveness of the two-color method established in this study, the NO_X reduction effect of direct water injection (DWI) system could be strongly backed up.

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The effect of swirler/prefilmer modules on spatially and temporally resolved gas temperature were experimentally investigated for better understanding of flame stability and flow structure. Temperature measurements were carried out by using coherent anti-Stokes Raman spectroscopy(CARS) at several positions within the aero-engine combustor sector rig burning standard kerosene fuel. Research rig representing a 36° sector from a full annular combustor was installed and run at simulated ground idle conditions, showing features of flow mixing within the burning rig. Inlet air was heated and compressed up to 530K and 3.2bar. Air flow rate and overall A/F ratio were 1.1kg/s and 90 respectively. Experiments were carried out at three conditions to see the individual effect of swirl direction and prefilmer. Temperature PDFs were obtained from 500-single shot spectra to investigate the temperature fluctuations in the combustor. Results revealed that a strong reverse flow zone is formed by the lean fuel module with radial swirler. And it also shows that swirl direction of fuel module significantly affects to the shape of recirculation zone, while the presence of prefilmer forms more uniform spray characteristics and pushes the recirculation zone in further downstream.

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Knocking combustion in SI engines is regarded as an auto-ignition of unburned gas, and it has been widely examined by using rapid compression machines (RCM) or test engines. Recent researches point out the importance of the low temperature reaction and negative temperature coefficient. To investigate the effect, measurements of instantaneous local gas temperature, visualization and pressure were conducted. Measurements using real engines are too difficult to analyze while those with RCM have not been made with flame propagation. Therefore, the authors aimed to make measurements under knock conditions where propagating flame exists during the induction time for auto-ignition using a constant volume vessel. Adopting the two-wire thermocouple method enables us to measure the local temperature until the moment when the flame front passes by without any interference. High-speed images inside the unburned region were also recorded simultaneously using an endoscope. As a result, it was found that when knock occurs, the ignition time seems slightly early compared to results without knock. Interference of hot spots may cause a higher gas temperature region and leading to knock due to a larger heat release by auto-ignition than by flame propagation when the initiation time of auto-ignition was accelerated for some reasons.

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Recently, some approaches based on genetic algorithms and neural networks have been applied for optimizing arbitrary constants in fluid-dynamic, chemical, and physical models. Here, combination of genetic algorithm and the intuition theory proposed by K. Naitoh automatically optimizes the auto-ignition model proposed by Halstead et al. First, the differential equations describing highly nonlinear chemical reaction processes of gasoline are optimized with genetic algorithm (GA). In some cases, ignition delay, the interval from compression start to ignition occurrence, can be accurately calculated by using the optimized constants. The intuition theory also clarifies whether the arbitrary constants are optimized by GA or not. It is understood by using this intuition theory that some of the arbitrary constants cannot be optimized. There are so many types of computational models predicting engine performance, which are based on zero-dimensional thermodynamic models, ensemble averaged flow simulators, and large eddy simulations. Arbitrary constants in the chemical reaction models must be varied for each computational model. The present automatic technique on optimization will bring us an important role for realizing virtual engines.

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The numerical simulation of Internal Combustion Engine (ICE) flows is a powerful tool which is widely applied for the engine design process. In particular, CFD simulation is useful at a preliminary stage in order to better understand how geometrical and operating engine variables can affect mixture flow features and, in turn, the combustion process. In a previous work, a comparison was carried out among three different versions of the k-e turbulence model (Standard and RNG two-equation models, Two-Scale four-equation model) through their application to the turbulence and mean-flow field prediction within the open chamber of a model engine in the absence of swirl. The RNG model, including a modified approach with respect to the Logarithmic Wall-Function boundary conditions, was shown to yield, on the average, a better agreement with experimental results than the other two models. The present paper is concerned with mean-flow and turbulence simulation in a motored model engine having an axisymmetric combustion chamber, one centrally located valve and each of a flat piston and cylindrical bowl-in-piston arrangements. Numerical results obtained with the RNG k-e model are first compared with available experimental data obtained in the presence of swirl. Subsequently, the main flow features predicted for the swirling flow configuration are compared to those obtained in the absence of swirl. Finally, the turbulence model capabilities in capturing in-cylinder flow features is assessed, by analyzing its prediction of the flow parameter variation when geometrical and operating engine variables are modified. The calculations are performed using a non-commercial CFD code that was originally developed in and updated for the present investigation. A finite-volume conservative implicit method is employed for the discretization of the partial differential equations modeling the in-cylinder turbulent flow. The resultant algebraic equations are linearized first and then sequentially solved by an iterative procedure based on a pressure equation, derived from the continuity equation, and on under-relaxation practices in order to improve stability.

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In order to numerically predict the combustion processes in homogeneous charge compression ignition (HCCI) engines and also conventional compression ignition engines with reasonable accuracy, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed kinetic models and also to the optimization of the model constants involved in the ignition and combustion models. By means of the present optimization method, a detailed kinetic model (592 reactions) for gasoline with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. A reduced reaction scheme (45 reactions) for dimethyl ether (DME) derived from Curran's detailed scheme has been proposed, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors' GTT code which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted the modified eddy dissipation combustion model. Schreiber's five-step reaction scheme has been optimized for DME, and the combustion process in a DME injection diesel engine has been simulated considerably well by three-dimensional simulation using the GTT code, into which this optimized simple reaction scheme and the modified Reitz's combustion model with the optimized chemical characteristic time scale have been incorporated. As a result, the effectiveness of the present optimization method by means of GA has been confirmed.

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Methanol was injected into the suction port of each cylinder in an ordinary direct injection diesel engine, and was ignited by a small amount of gas oil as an ignition source. The effects of the equivalence ratio of methanol, the injection amount and the injection timing of gas oil, the intake temperature and the compression ratio on ignition, the maximum burning rate of methanol mixture and the knock limit were investigated experimentally. It is found that the maximum burning rate of methanol is almost independent on the intake temperature until knock onset, then, the burning process of methanol is "flame propagation". As results, a marked improvement in the trade-off between NO_x and smoke was achieved maintaining a high thermal efficiency by a suitable combination between the parameters mentioned above for each engine load further adopting the high EGR rate and the small orifice size nozzle as well.

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Recently the heavy duty diesel engines have adopted the direct fuel injection combined with high injection pressure, the high boost turbo charger and the EGR, which is well known as a means to reduce the emissions effectively. The experiment has been done under the conditions of intake air quantity up to 4 times of naturally aspirated (NA) engine, 250MPa injection pressure and 70% EGR ratio. In these conditions the exhaust emissions such as NO_X and smoke are effectively decreased.

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Employing a direct-injection diesel engine equipped with a common-rail type of injection system, adding formaldehyde (CH_2O) to the intake air, and changing the fuel-injection timing, the compression ratio and the intake-air temperature, a mechanism for CH_2O as a fuel additive to affect auto-ignition was discussed. Unlike an HCCI type of engine, the diesel engine can expose an air-fuel mixture only to a limited range of the in-cylinder temperature before the ignition, and separate low- and high-temperature parts of the mechanism. When low-temperature oxidation starts above 900 K, there are cases where the CH_2O advances the ignition timing. Below 900 K, to the contrary, it always retards the timing. It is because above 900 K, a part of the CH_2O is changed into CO and H_2O_2 as an ignition promoter. Below 900 K, on the other hand, the CH_2O itself acts as an OH radical scavenger against cool-flame reaction, from the beginning of low-temperature oxidation. Then, the engine was modified for its extraordinary function as a gasoline-knocking generator, in order that effect of CH_2O on knocking could be discussed. The CH_2O retards the onset of auto-ignition of an end gas. Judging from a large degree of the retardation, the ignition is probably triggered below 900 K.

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This study investigated deNO_X mechanism caused by thermal cracking hydrocarbons during diesel combustion experimentally and theoretically. Experiment using a rapid compression machine and a total gas-sampling device shows that NO_X can be reduced during second half of diffusion combustion under rich and high swirl condition. Under this condition, stratified rich region is distributed in the combustion chamber. Thermal cracking hydrocarbons are locally accumulated in this region. Moreover, it is shown that a large amount of thermal cracking hydrocarbons are produced during ignition delay period and at initial combustion stage. These hydrocarbons mainly consist of unsaturated hydrocarbon such as C_2H_4. At diffusion combustion stage, CH_4 becomes main hydrocarbon. A flow reactor system was used to investigate thermal cracking process of diesel fuel and NO_X reduction process. It is found that about 60% NO_X can be reduced under rich and high temperature condition. The condition is at equivalence ratio of over 2.5 and temperature of 1500K in this study. When C_2H_4 is introduced as fuel, NO_X can be further reduced up to 80%. It is indicated that C_2H_4 plays an important role in NO_X reduction. Chemical kinetic calculation using CHEMKINHI reveals the deNO_X mechanism. C_2H_4 is easily decomposed as compared with CH_4. During the oxidation process of C_2H_4, NO_X is reduced through the reaction of HCCO or CH_2 with NO. In this reaction path C_2H_2 is an essential species to form HCCO and CH_2. C_2H_2 is one of thermal cracking hydrocarbons and also formed through thermal cracking process of C_2H_4.

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Numerical simulations and experiments have been carried out to investigate the effect of fuel injection nozzles on the combustion and NO_X formation processes in medium-speed marine diesel engines. Spray and combustion phenomena were examined numerically using FIRE code. Wave breakup and Zeldovich models were adopted to describe the atomization characteristics and NO_X formation processes. Spray visualization experiment was performed in the constant-volume high-pressure chamber to verify the numerical results on the spray characteristics such as spray angle and spray tip penetration. Time-resolved spray behaviors were captured by high-speed digital camera and analyzed to extract the information on the spray parameters. Numerical analysis of fuel injection system was also performed to get the profiles of fuel injection rate, which should be given as an input data for the combustion analysis. Numerical results were verified with experimental data such as cylinder pressure, ROHR (Rate of Heat Release) and NO_X emission. Finally, the effects of fuel injection nozzles on the engine performance were investigated numerically to find the optimum nozzle parameters such as fuel injection angle, nozzle hole diameter and number of nozzle holes. From this study, the optimum fuel injection nozzle (nozzle hole diameter, 0.32 mm, number of nozzle holes, 8 and fuel injection angle, 148°) was selected to reduce both the fuel consumption and NO_X emission. The reason for this selection could be explained from the highest fuel-air mixing in the early phase of injection due to the longest spray tip penetration and the highest heat release rate after 19° ATDC due to the increased injection duration.

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Due to the toxicity of ammonia generally used as a reducing agent in SCR system, urea solution, which is decomposed into ammonia (NH_3), was adopted in our system instead of ammonia. It is necessary to make the system compact because of the narrow space for installing it in the ship. Urea is thermally decomposed into ammonia in the mixing chamber where it is sprayed by nozzle. In this study, urea decomposition in hot gas was investigated for the optimum design of the mixing chamber in SCR system. Tests were accomplished at various temperature ranges and gas flow rates. The reaction equation for thermal decomposition of urea was derived. Also, the experimental results were verified by comparing to those of the CFD with the equation.

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In diesel combustion it is commonly known that NO_X emissions increase when the fuel injection velocity increases. On the other hand, increased fuel velocity reduces NO_X in steady jet flames, due to a decreased residence time in the flame region. To answer this contradiction, the authors have made variety of experiment and numerical simulation. The results indicated that the large NO_X formation in diesel engine is due to the weak mixing intensity in the spray tip region, where the flow and turbulence structure is quite different from the continuous jet flames. The fact indicates that there is a possibility of reducing NO_X from diesel engines by enhancing mixing intensity at the spray tip region to the level of continuous jet flame. As one of the attempts to make the velocity profile of diesel spray similar to the steady jet, an inert gas is injected prior to the fuel injection. Figure 1 shows an experimental result comparing the flame appearance and NO_X emission index between the cases with and without a nitrogen injection prior to the propane injection. The flame apparently becomes less luminous by the pre-injection of nitrogen, and the NO_X emission index is two-thirds of the non pre-injection case. Figure 2 is the result of numerical simulation, showing the effect of pre-injection period and types of gases for the reduction of NO_X. It is seen that NO decreases with the increase of the pre-injection period, although the maximum temperatures are almost constant in all cases. This suggests that the NO_X reduction is not due to the temperature difference but due to the enhanced mixing and decreased residence time at high temperature by the pre-injection. The paper will present the above results together with photographic analysis of enhanced mixing of spray tip region by pre-injection of water.

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The paper gives an analysis of solutions of turbocompound action: mechanical and electrical. Traces of power obtained by the turbine and power demand for driving the air compressor are also shown. A graphic presentation of power that maybe recovered from exhaust gases energy by application of these systems is also given. The last part of the paper contains conclusions on turbocompound systems and their advantages.

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The article contains an analysis of a turbocharger model in witch gas bearings were applied. It also gives the measurement results of oil consumption by a turbocharger equipped with a normally used bearing system of a turbocharger. A mathematical model for calculation caring capacity of gas bearings in application to turbocharger was presented in this paper. The article gives also the measurement method of oil consumption by the turbocharger in variants ranges of engine work. Application of such bearings aims at: - elimination of oil penetration from turbocharger intata spaces in the compressor body and turbine. Elimination of these leaks caused a decrease in toxic component concentration in exhaust gases. A significant decrease in the amount of hydrocarbon and a considerable reduction of solid particles is note worth. This problem is specially significant as concerns protection of the natural environment harmed by the ever increasing number of vehicles driven by internal combustion engines with turbocharger. - Application of gas bearings permitted to diminish the moment of friction in the bearing shell of the turbocharger shaft, this has a positive influence on the reaction time of the torbocompressor system. Application of a new type of bearing reduces also the masses of the compressor and this has a positive effect on shortening of the reaction time of the turbocharger. - Reduction of friction in the bearings shells permits to increase the rotational speed of the turbocharger and rotor - Bearings of the new structures should contribute to smaller dimensions of the turbocharger and this will make its housing at the engine easies.

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The objective of this study is to investigate the relationship among heat loss through the chamber wall of diesel engines and the spray flame impingement on the wall, the flame motion and the combustion characteristics such as flame temperature and rate of heat release. Local heat flux at 6 locations on the piston head of a rapid compression and expansion machine, by which experimental conditions such as injection conditions, ambient conditions, can be independently controlled, were measured by thin film thermocouples. The spray flame in an optically accessible combustion chamber with a quartz piston head was imaged by a digital high speed camera to observe the flame motion. From the high speed direct photographs, flame temperature distribution was obtained via two-color method. These measurements were conducted with changing the nozzle orifice diameter of fuel injector and the swirl ratio to investigate the effects of relative flame motion to the chamber wall on the heat loss. The ambient oxygen concentration was also changed as parameter to investigate the effects of combustion characteristics including flame temperature, ignition delay, combustion duration, and rate of heat release, which are affected significantly by oxygen concentration, on the heat flux on the chamber wall. Experimental results showed that the magnitude of heat flux is determined mainly by flame temperature and the relative distribution of heat flux is determined by the distribution of high temperature region in the flame. However, at flame impinging region on the wall, flow motion induced by the spray contributes to increase in heat flux. As nozzle orifice diameter is decreased, average flame temperature is increased, however, local heat flux at the bottom of the piston cavity decreases due to decrease in spray flame penetration. As ambient oxygen concentration is decreased, average flame temperature decreases, and this results in the decrease in local heat flux in the piston cavity. On the other hand, the relative distribution of heat flux is not affected by ambient oxygen concentration. The distribution of heat flux on the piston cavity wall is strongly affected by the swirl motion because the relative flame location to the chamber wall is changed significantly by the change in swirl ratio.

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The heavy duty diesel engines have adopted many technologies for clean emissions and low fuel consumption, such as direct fuel injection combined with high injection pressure and adequate in-cylinder air motion, turbo-intercooler system and highly strong steel piston. By these technologies the diesel engines have achieved the one of the lowest CO_2 emission as prime mover. However the heavy duty diesel engines are strongly expected lower NO_X and PM emission levels than today. In this study the high boost and lean diesel combustion has been attempted by a single cylinder engine in order to obtain a good engine performance and clean exhaust emission. The experiment has been done under the conditions of intake air quantity up to 5 times of naturally aspirated (NA) engine and 200 Mpa injection pressure. The adopted pressure booster is external supercharger, which can control intake air temperature. In this engine the maximum cylinder pressure will increase and new technologies have been adopted, such as the monotherm piston for the endurance of Pmax 30 Mpa and also every engine part is designed newly. As the boost pressure increase, the rate of heat release is resemble to the injection rate and becomes sharper and combustion improves and also the brake thermal efficiency becomes better. The high boost and lean diesel combustion results in low smoke, ISCO and ISTHC without the ISNO_X increase and gives good thermal efficiency.

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A parametric study of automotive diesel combustion in a low-temperature, late-injection combustion regime is described. Injection pressure was varied from 600-1200 bar, swirl ratio from 1.44-7.12, and intake temperature from 30-110°C. In-cylinder pressure records, heat release analysis, spatially-integrated soot luminosity, and images of the spatial distribution of combustion luminosity are employed to study the influence of these parameters on the combustion and soot formation/oxidation processes. Load points of 3 and 6 bar gross IMEP at 1500 RPM and an O_2 concentration of 0.15 are considered. Increased injection pressure is found to enhance the early mixture formation process, resulting in increased peak apparent heat release, generally decreased soot luminosity, and modestly increased light-load soot oxidation rates. At lower injection pressures, more soot luminosity is observed from the squish volume. In contrast, variation of flow swirl impacts the latter half of the combustion process, and affects the initial combustion only slightly. An optimum Ricardo swirl ratio of roughly 3 is found for best moderate-load efficiency and soot oxidation. A marked reduction in early heat release rates and peak soot luminosity is observed with decreased intake temperature. Nevertheless, significant incylinder soot luminosity is observed even at the lowest intake temperatures, indicating that complete suppression of incylinder soot formation is difficult with the fuel injection and combustion system characteristics employed.

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A cycle simulation program has been developed for mathematical model of compression ignition engine. Models for the prediction of combustion and heat transfer have been formulated and developed. Annand's and WOSCHNI'S heat transfer have been considered for the calculation of gas-wall heat transfer. Models for delay period and wall heat transfer have been formulated and developed and coupled along with the above combustion and gas-wall heat transfer model to predict the effect of varying wall temperature on combustion, heat release, heat transfer and overall performance of a low heat rejection direct injection diesel engine. Two different ceramic insulation coating material like zirconia and silicon nitride of 0.5 mm and 1 mm thickness coating on combustion chamber are considered for insulating combustion chamber. (Insulating combustion chamber includes crown of the piston, cylinder head, valves and liner) In the present work, effect of varying different injection tuning on combustion, rate of heat transfer, cumulative heat transfer, delay period, varying temperatures of piston, cylinder head and liner using with and without insulated combustion chamber have been considered and critically analyzed overall performance of the LHR and conventional diesel engine.

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This work investigates the soot formation process in diesel jet flame using a detailed kinetic soot model implemented into the KIVA-3V multidimensional CFD code. The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver using Message Passing Interface (MPI). This allows for the chemical reactions to be simulated hi parallel on multiple CPUs. The detailed soot model used is based on the method of moments, which begins with fuel pyrolysis, followed by the formation of polycyclic aromatic hydrocarbons, their growth and coagulation into spherical particles, and finally, surface growth and oxidation of the particles. The model can describe the spatial and temporal characteristics of soot formation processes such as soot precursors distributions, nucleation rate and surface reaction rate. Simulation results show that the soot particles are formed to surround the soot precursor formation region and to extend downstream. It was also found that the dominant soot growth process differs by the region in the fuel jet. The particle inception is fast around the central region of the jet, and acetylene surface reaction rate becomes higher toward the periphery of the jet.

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In this paper, we will briefly review the soot modeling approaches that have been proposed for diesel combustion studies. Beginning from Hiroyasu's model, to Fusco's model, and then to a complex-chemistry coupled phenomenological model, we will compare the results predicted using these three models for one engine case, and put the future application of soot modeling into perspective.

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The effects of the spray impinging part and swirl ratio on the in-cylinder airflow were numerically analyzed in the combustion chamber of the impinging diffusion direct injection diesel engine using KIVA-3 code. KTVA-3 code was enhanced to cater the impinging part as an internal obstacle by adopting the virtual droplet method, which is relatively easy to implement. Numerical result shows that the turbulence generation is promoted by the impinging part and is transformed by the squish flow into the piston cavity. The secondary flow is generated beneath the impinging part as well. The secondary flow area increases as the distance between top surface of the impinging part and bottom surface of the cylinder cover increases. It also increases as the swirl ratio increasing.

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Three dimensional calculations of a split injection in DI Diesel engine were performed using the KIVA3V, release 2, CFD code. The detailed chemistry approach used involves the Partially Stirred Reactor (PaSR) model for the turbulence-chemistry interaction coupled with the chemical mechanism of a diesel fuel surrogate represented by a mixture of n-heptane and toluene (68 species, 270 reactions). When simulating the Volvo NEDS DI Diesel engine in a split injection mode, it was found that the droplet collisions play a considerable role in predicting the rate of heat release during the pilot injection. It was found that if a collision probability is over-predicted, it causes a droplet cluster formation and too fuel lean conditions resulting in a decrease in combustion intensity. The default collision model in the KIVA3V code, formulated by O'Rourke, is replaced by the modified model proposed in Nordin. The O'Rourke model formulation defines collision frequency inverse proportional to the cell volume that causes grid dependence and does not discriminate droplet trajectories which are not intersecting each other. In a new grid independent formulation, two vital requirements have to be met for collision between two droplets to occur: first, they have to travel towards each other being in a so-called "collision" cone and second, all colliding droplets are constrained to a certain exponential time-decaying initial probability in the Poisson law. Using the new formulation, higher combustion intensity was achieved during the combustion.

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The new eddy dissipation concept (EDC) model based on the operator-splitting procedure applied to the mass conservation equations for species participating in reversible chemical reactions representing combustion in a PaSR partially stirred reactor (PaSR) volume is analyzed. The model has been implemented in the KTVA-3V code together with a new droplet collision procedure, and its application to spray combustion simulation is illustrated by the results of the 3-D modeling of the DI Diesel Volvo D12C engine. The chemical mechanism of diesel oil surrogate consisted of 68 species (including soot aromatic precursors) participating in 285 reversible reactions has been applied to simulation of MK (Modulated Kinetics) diesel spray combustion regime. Mean features of MK combustion under conditions of delayed injection when auto-ignition has much in common with the HCCI process are predicted in accordance with experimental data.

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The 3-D CFD code could be a very useful tool to predict diesel combustion and emissions formation and reduction. The code is required to reproduce phenomenological processes such as atomization, evaporation and mixing with air. In addition, detailed chemistry should be taken into account for modeling combustion. For this purpose, in the present study, the hybrid Kelvin-Hehnholtz/Rayleigh-Taylor droplet breakup sub-model is introduced to describe spray atomization characteristics under high pressure and temperature conditions. The sub-model based on the Partially Stirred Reactor (PaSR) is also used to represent the interaction between turbulent mixing and detailed gas phase chemical kinetics. These sub-models are then improved and validated by comparing with experimental results.

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Fuel injection characteristics play a decisive role in small bore sized DI diesel engines in the performance characteristics, in-cylinder thermal / mechanical stresses and formation of nitric oxide and soot. This paper reports on investigations using Computational Fluid Dynamics (CFD), carried out to evaluate various schemes of pre-injection rate shaping at an idling speed of 900 rpm. The fuel considered for the combustion analysis is n-heptane. The main emphasis is on split injection, typically employed in Pressure Controlled (PC) injectors. The fuel injection schemes comprise a pre-injection pulse before compression Top Dead Centre (TDC) followed by a main injection pulse starting at compression TDC, with both the pulses separated by a dwell period. A nozzle Needle Lift Controlled (NLC) injection rate shaping scheme used in common rail fuel injection systems is also analysed computationally. In-cylinder spatial velocity profiles during combustion, and heat release rate profiles subjected to validation agree reasonably well with experimental data available in open literature. From the pressure based results it is concluded that the scheme with 50% pilot injection quantity with 3 to 6 crank angle degree dwell period showed higher peak pressures and decreased combustion duration. The decreased combustion duration is indicative of enhanced mixing, likely induced by the rapid gas expansion of a larger proportion of premixed burn. Soot - NO_X trade-off analysis revealed the NLC injection scheme to be highly advantageous over other split injection schemes at low load.

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Formaldehyde artificially added into the mixtures is efficacious as an ignition control medium for hydrocarbon fuels in engine cylinders. The vapor added into the mixtures has given the premixed compression-ignition (HCCI) engine a stable ignition timing, which is controllable to get the MET by the amount of formaldehyde to be added. The effect of formaldehyde addition is either suppressing or promoting. A universal criterion of the formaldehyde effect resulting whether in the advanced or in the retarded hot-flame appearance from the original ignition events has been elucidated through experiments over a wide range of parameters on the fuel octane or butane rating, the equivalence ratio of the mixture, and the mixture temperature to be raised. The formaldehyde would be a suppressing additive under the cool-flame generating constituents, temperature and pressure conditions, and a promoting additive under the poor cool-flame generating conditions in the cylinder charge during the preflame reactions leading to the ignition. The added formaldehyde is superfluous to the ignition event originally belonging to the cool-flame dominant regime, which would give a suppressing effect. On the other hand, the artificially added formaldehyde could be a starting point of preflame reactions leading to the final hot ignition belonging to the blue-flame-dominant regime, where a few fuel transition and low intermediates appear, and where the high temperature chemistry dominates. It allows a short cut of the preflame induction period, in consequence, a promoting effect for the ignition. The low-temperature-ignition classification; three typical regime, "cool-flame dominant regime", "negative-temperature-coefficient regime" and "blue-flame dominant regime" would be a universal advanced/retarded criterion on ignition of fuel/air mixtures with formaldehyde doping for the ignition timing control in the piston compression engines.

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The control of ignition timing and combustion period over a wide range of engine speeds and loads in HCCI engine is one of the barriers to the realization of the engine. Application of exhaust gas recirculation, EGR, is thought to be a promising option to control ignition timing, to extend combustion period and to suppress knock like combustion. In this study, the effects of N_2/CO_2, major components of exhaust gas, addition on the heat release of cool flame and the emission characteristics of CO were investigated from experiments and computations. The heat release of cool flame was reduced with N_2 addition, however, it increased with CO_2 addition. From the systematic experiments and chemical kinetic computations, it was confirmed that the amount of heat release at cool flame depends strongly on the concentration of O_2 at cool flame onset. The dominant path for CO oxidation is the reaction of CO + OH = CO_2 + H. The produced H atoms react with O_2 molecules and produce OH + O or HO_2. The CO oxidation becomes active as increasing the blanching rate to OH + O. However, with the addition of CO_2 to the mixture, the branching rate to HO_2 was increased, resulting in a higher CO emission. Though the addition of CO_2 is effective in suppressing a knocking from its large heat capacity, it has an inferior effect on CO emission.

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Controlling ignition timing in the homogeneous charge compression ignition (HCCI) of dymethyl ether (DME) by adding methanol and ozone has been studied in a motored engine. In the standard pressure, temperature and rate of heat release analyses in two-stage ignitions, reduction of the first stage (cool ignition) heat release with methanol addition and consequent retardation of the second stage (hot ignition) was confirmed. Composition analysis, conducted under moderate, single cool ignition conditions, exhibited liner reductions of fuel consumption and formaldehyde formation, while maintaining their ratio as 1:1. These observations were well reproduced by the detailed chemical kinetic model of Curran et.al. for DME oxidation at every examined equivalence ratio. A simple formulation accounting for the retarding effect was established, in which HCHO + OH and methanol + OH reactions are responsible for the termination of DME chain reaction system of low temperature oxidation. In contrast, acceleration with ozone addition was caused by increase of heat releases in the cool ignitions taking place at a lower temperature, while the thermal ignitions begin at a constant temperature. The cool ignition composition analysis showed increases of fuel consumption and formaldehyde formation, whereas the formaldehyde increase is less significant at a higher addition of ozone. Inclusions of ozone decomposition forming O + O_2 into the model enabled a good reproduction of these features. It was inferred that the early radical supply from ozone reduced the cool ignition onset temperature significantly, where a stable intermediate accumulates owing to slow decomposition, and that the resultant reduction of formaldehyde formation induced the longer chain duration.

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Experiments and a CFD analysis have shown that the charge mixture in a premixed charge compression (PCCI) engine with direct in-cylinder injection early in the compression stroke is still heterogeneous even at the compression end. Although improvements in homogeneity do not always result in low emissions, elimination of regions having a near stoichiometric mixture ratio, where NO_X formation is significant, is essential to realize ultra low emissions. Fuel volatility has a strong influence on the mixture formation process in a direct injection PCCI engine. Direct injection of a low volatility fuel, such as diesel fuel, early in the compression stroke results in adhesion of unevaporated fuel on the cylinder liner wall. This undesirable condition results when the fuel distillation temperature is higher than the temperatures of the in-cylinder gas and cylinder liner wall. Fuel adhering to the wall is also drawn into the crankcase where it dilutes the lubricant oil. If the quantity of fuel wall-wetting becomes large, lubricating oil dilution becomes a serious problem in practical applications. It may be possible to improve both mixture formation and homogeneity, and decrease wall-wetting by using higher volatility fuels with distillation temperatures lower than the in-cylinder gas temperature early in the compression stroke. This research addressed the potential for improvements in early direct injection type PCCI combustion with a higher volatility fuel, experimentally and computationally. The combustion and emissions in a PCCI engine with a higher volatility fuel and with ordinary diesel fuel were compared to establish the effect of distillation temperature, and the mixture formation processes of the early stage injection were analyzed with a CFD model. A normal heptane + isooctane blended fuel with ignitability similar to diesel fuel in PCCI operation was used as the higher volatility fuel. The quantity of fuel lost to lubricant oil under several fuel injection conditions was measured for the normal heptane + isooctane blend and for the ordinary diesel fuel by determining fuel components in the used lubricant oil. The experimental results showed that the deterioration in thermal efficiency that occurs with advanced injection timings with ordinary diesel fuel could be eliminated with the higher volatility fuel without significantly altering the THC and CO emissions. With early injection timings, the rate of heat release with diesel fuel is smaller than with higher volatility fuels. This result suggests that with diesel fuel there is significant fuel adhesion to the cylinder liner wall and also absorption into the lubricating oil. The CFD analysis showed that the normal heptane + isooctane blend fuel improves the homogeneity of the mixture, probably due to the higher volatility. The analysis of components in the used lubricant oil showed that a remarkable quantity of diesel fuel, corresponding to 7% of the total energy supply, is lost to the lubricating oil when the fuel spray is allowed to impinge directly on the cylinder liner wall. The higher volatility fuel effectively reduces fuel adhesion on the cylinder liner wall and prevents fuel absorption into the lubricating oil even with early injection timings when the fuel is allowed to impinge directly onto the cylinder liner.

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Research and development in the field of gasoline engines today have to face a double challenge: on the one hand, fuel consumption has to be reduced, while on the other hand, ever more stringent emission standards have to be ful-filled. A very promising technology for simultaneous achievement of both ultra-low emissions and a high fuel economy is HCCI (Homogeneous Charge Compression Ignition) combustion. For the present study, a single-cylinder SI research engine has been modified for homogeneous compression ignition combustion by applying special cam profiles and variable exhaust cam phasing. The engine has been run both in port injection and in direct injection mode at varying operating points with different air-fuel ratios and residual gas contents. In addition to the thermodynamic analysis of the combustion process at various injection timings, the residual gas content has been examined using a gas sampling valve. Besides, optical investigations have been carried out using an endoscopic multi-fibre visualization system with a high temporal resolution for cycle-resolved analysis of the ignition and combustion process. For the numerical investigations, the engine has been modeled in one- and three-dimensional CFD codes. The gas exchange process has been analyzed and optimized by one-dimensional calculations. Three-dimensional CFD calculations of in-cylinder flow and mixing processes have been carried out with the aim of analyzing the distribution of fresh charge and residual gas and the overall homogeneity of the cylinder charge obtained as a result of the gas exchange process. The combined approach applied in this study gives new insight to the nature of combustion by homogeneous compression ignition.

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A premixed charge compression ignition(PCCI) combustion was simulated by the Large Eddy Simulation in conjunction with a reaction kinetics model. We analyzed the interrelationships between mixture heterogeneity and reaction in a turbulent flow. Several different initial conditions of heterogeneity of an air-fuel or air-fuel-EGR gas mixture were given at the intake valve closing time by a new method, which generated a statistically reasonable turbulent fluctuations in both velocity and fuel mass fraction fields. The auto-ignition and combustion behaviors were analyzed for several different sets of the rms and the length scale of the fluctuations in fuel mass fraction. The analyses show that the equivalence ratio fluctuations with large rms and length scale have considerable effect in attaining moderate combustion in a PCCI engine.

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In this research, the influence on natural gas combustion of H2 and CO was investigated by numerical calculations with elementary reactions. The investigation was carried out using the following procedures: 1. To research basic oxidation characteristics of CH_4/H_2/CO mixed fuel, parametric calculations for initial temperature were carried out. 2. For investigation of the effect of H_2 and CO on CH_4 combustion, the calculations with H_2 and CO initial mole fraction variation was carried out. As a result, it was clarified that the oxidation temperature of CO was higher than that of CH_4 and H_2, the increase of H2 initial fraction has the effect to advance CH_4 ignition tuning, and increase of the CO fraction, under the condition that only CO was added, has the opposite effect of H_2 addition.

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To extend the available load range and obtain higher thermal efficiency in natural-gas PCCI engines, the strategy for controlling direct-injection combustion was discussed. Experimental results from single-cylinder engine tests show the possibility of extending load range by direct fuel injection. Reduced nozzle orifice size and reduced injection angle provide higher combustion efficiency; however, promotes knock because of the formation of locally rich mixture. From the discussions based on the prediction by CFD code considering mixture heterogeneity, it is suggested that controlling PDF of fuel concentration could be a means to control the rate of pressure rise.

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Controlling the autoignition timing over a wide range of speeds and loads is challenging. Overcoming this challenge to practical HCCI engines requires an improved understanding of fie in-cylinder processes and how these processes can be favorably altered by various control techniques. In the current study, a zero-dimensional thermodynamic model that contains a simple heat release sub-model and an autoignition model was used in a predictive fashion to better understand in-cylinder processes and the efficiency potential of a natural gas engine in HCCI mode. The model was also used for parametric studies to evaluate HCCI control strategies that can be tested on the research engine. The results indicated that if initial conditions of the mixture are known precisely at intake valve closing, the autoignition timing is controllable. The thermal efficiency close to 0.45 is possible with an IMEP range from 4 to 5 bar for the described engine, also.

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A rotary slit valve of 20 x 1mm has been designed to produce a transient flat liquid sheet. It operates with the same fuel delivery pressures as GDI injectors with the long term vie w of conducting a detailed comparison between transient flat and conical liquid sheets. The current work has focused on the pressure range from 10-50 bar. First generation pressure swirl GDI injectors typically operate at a fuel pressure of 50 bar. This study describes the liquid sheet break up phenomena of the transient two dimensional liquid sheet using CCD macro-imaging, Particle Image Velocimetry, PIV, and Laser Doppler Anemometry, LDA. The transient liquid sheet break up behaviour has been assessed from a detailed analysis of the CCD images. The propagation of surface waves and structures downstream from the nozzle as a function of time have been measured by a modified PIV technique. The local velocities of the intact liquid sheet, the remnants of the sheet after break up and droplets due to atomization at various axial positions downstream from the nozzle slit have been measured using LDA to provide the time averaged histories of the liquid velocity.

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Experimental investigations of fuel breakup very close to nozzle of practical high-pressure swirl injector, which is used in direct injection spark ignition (DISI) engine, were carried out. In DISI engines, fuel is directly injected into cylinder therefore the spray characteristics and mixture formation are of primary importance. Many experimental investigations using several measurement techniques like laser sheet method with high-speed camera, LIF or PDA have been carried out for better understandings of spray and combustion characteristics. However, experimental investigations of atomization process were restricted due to very high-speed and very small region phenomena. Although scale-up models have been used to study the primary spray structure, it is impossible to match Reynolds, Weber, and cavitation numbers and time scales in practical high-pressure swirl injector. Microscopic investigation of primary spray structure of practical swirl injector is needed. On the other hand, numerical simulations have been conducted for better understanding of spray formation process. These researches indicated qualitatively good agreement, but the initial conditions, such as liquid sheet thickness and break-up length, were not accurately since break-up process of the liquid sheet from swirl injector has not been examined. In numerical simulation of spray behavior, a sub-model for atomization phenomena is very important. Therefore the primary atomization process and the break-up process of liquid sheet play an important role. In this research, visualizations of primary spray formation process were demonstrated using a high-speed video camera (maximum speed: Imfps) with a long-distance microscope. Initial state and development of the spray were discussed under the different ambient (back) pressure condition. During the injection period, the length and thickness of the liquid sheet, which is produced from the nozzle exit, were measured using Ar-ion laser sheet and high-speed camera. Moreover, fluctuations of the length and thickness of liquid sheet were discussed. Three main conclusions were drawn from this study. (1) It has been shown that the liquid fuel column without swirl motion was injected as a compact jet at the beginning of the injection. During the injection period, the spray indicates the quasi-steady state mode. (2) Liquid film sheet has a ligament structure. Using Ar-ion laser sheet and high-speed camera, length and thickness of the liquid sheet can be measured. (3) Surface waves of liquid sheet can be recognized. Higher ambient (back) pressure makes shorter wavelength of surface waves of liquid sheet of swirl injector.

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