Since the invention of spark ignition engines, knocking has been the limiting factor in the development of new engines with increased power density and improved efficiency. The mechanisms that lead to knocking combustion have been investigated in numerous research studies that have produced, to some extent, controversial theories. Even though it is very certain that knocking involves a detonation caused by self-ignition processes in the end-gas region, there is a great interest in growing the understanding of knocking phenomena and the associated multitude of combustion irregularities. This article gives an overview of the contemporary state of knowledge of knocking and other irregular combustion phenomena. In order to present the current understanding of knocking and combustion irregularities, historical knocking investigations, meaningful work on knocking in the last two decades of the previous century, and contemporary investigations are examined. In addition, this article discusses the information that remains unknown and the areas in which further research and development are necessary, so that today's questions about these phenomena can be answered in the future. For the purpose of describing and evaluating knocking and other combustion irregularities, not only experimental investigations will be employed, but also theoretical considerations.

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Chemical kinetic modeling of autoignition of practical fuels in internal combustion engines has made great advances in recent years. Practical transportation fuels are usually mixtures of very complicated, large fuel molecules which require extremely complex reaction mechanisms, and autoignition of these fuels is perhaps the most difficult and challenging problem to simulate. The kinetic reaction mechanism must be correct in both the low temperature and high temperature regimes, and these problems cover wide ranges of pressure, temperature, and fuel/air equivalence ratios. They also include some fascinating puzzles in kinetic theory and theoretical chemistry. The present paper describes recent progress in building kinetic models for reference fuels and other components of practical transportation fuels.

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Southwest Research Institute has demonstrated the ability of high levels of cooled EGR to significantly improve the fuel consumption of a positive ignition engine by reducing thermal losses, suppressing end gas knock and decreasing pumping losses. High levels of EGR dilution also simultaneously reduce the emissions of NOx, CO, and particle emissions across the full operating range of the engine. However, the use of cooled EGR has several challenges, including a reduction in combustion rates, decreased stability, lower combustion efficiency, and increased demands on the air handling system. A new concept for configuring engine hardware, called Dedicated EGR (D-EGR), was proposed in a previous publication to reduce many of these deficiencies and increase the fuel consumption benefit from cooled EGR. However, in the 4-cylinder application discussed in the previous work, the engine suffered from imbalances due to the pulsing nature of the Dedicated EGR loop. In this work, the D-EGR concept was pushed to the extreme. A V6 engine was configured to run with 50% EGR by using 3 of the 6 cylinders in D-EGR mode. A series of 1-D simulations was undertaken to investigate the potential to achieve the desired torque curve in D-EGR mode, examining single-stage and two-stage boosting with combinations of superchargers and turbochargers. An investigation of the dilution tolerance of various high energy ignition systems was performed to meet the aggressive 50% D-EGR target. Then engine was then demonstrated to operate with 50% D-EGR and the improvement in fuel consumption was documented at a series of part load conditions. The results show that this technology has considerable potential for high efficiency applications.

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To clarify the mechanism of high brake thermal efficiency of HCCI combustion compared to SI combustion, the contributions of pumping loss, friction loss and gross indicated thermal efficiency were investigated. Also, independent effects of heat loss, specific heat ratio, heat release profile and combustion timing on gross indicated thermal efficiency in HCCI combustion were analyzed in detail. As a result, high gross indicated thermal efficiency is found to be the main contributors to improvement in brake thermal efficiency. Also, it is found that heat loss in HCCI combustion is lower than SI combustion leading to the increase in gross indicated thermal efficiency. The improvement in gross indicated thermal efficiency in HCCI operation is mainly caused by lower heat loss in HCCI compared to SI combustion.

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For further improvement of thermal efficiency, it is necessary to focus on reducing cooling loss and exhaust loss aggressively. In this research, applying a CAE analysis coupling a 0-dimensional combustion analysis and a 1-dimensional heat conduction analysis, the influence of combustion chamber surface conditions such as heat conductivity, specific heat and engine specifications was parametrically investigated. Based on these results, the thermal efficiency and fuel economy improvement potential were unveiled.

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This paper proposes a new diesel combustion concept that achieves high thermal efficiency without deteriorating emissions. This new combustion is characterized by the reduction of the heat transfer coefficient through restriction of in-cylinder gas flow using a zero swirl port and a lip-less shallow dish combustion chamber. Since restricting the gas flow generally causes an inadequate mixture of fuel and air, a micro multi-hole injector was adopted to create highly dispersed fuel spray that improves the air-fuel mixture. The temperature gradient near the combustion chamber wall was reduced by moving the combustion area to the center of the combustion chamber. This was achieved because the fuel spray created by the micro multi-hole injector has weak penetration. These improvements reduced the heat flux from the in-cylinder gas to the surface of the combustion chamber wall and improved the cooling heat loss. The heat flux was also analyzed to further reduce the cooling heat loss. This analysis found that providing a taper at the upper portion of the combustion chamber reduced the heat flux generated by the reverse squish flow. By combining all of these elements, namely the low-swirl port, tapered lip-less combustion chamber, and micro multi-hole injector, a 5% reduction in fuel consumption was achieved compared to conventional combustion, without an emissions penalty.

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Exhaust heat recovery of automobile using thermoelectric generators (TEGs) has strong potential for improving fuel economy. In this study, simulation was performed to estimate the fuel economy improvement using an exhaust heat recovery system with thermoelectric generators in a series hybrid. The study investigates on fuel economy benefit from electrical power generation along with quick warm-up of engine due to heat transfer from exhaust gas to coolant accompanied with power generation and estimates benefit of TEGs against future fuel economy regulations. It is concluded that electrical output generated by TEG using exhaust heat and quick warm-up of engine coolant could yield an improvement of about 3% in fuel economy in US 5 cycles fuel economy, and additional benefit toward future Corporate Average Fuel Economy (CAFE) and Greenhouse gas (GHG) regulations could be expected.

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The engine's main specifications are six cylinders in-line and 10.5 liter displacement with a turbo-intercooled and cooled EGR system. The pressure ratio of the turbocharger installed in this test engine can be 5.0 higher than 3.0 of current ones. The EGR system consists of both a high-pressure loop (HP) EGR and a low-pressure loop (LP) EGR. The combination of these EGR systems reduces NOx and PM emissions effectively in both steady-state and transient conditions without a fuel consumption penalty. The common rail system adopted in the engine can produce 220 MPa in maximum injection pressure. The emission target has been clarified by a combustion improvement and an aftertreatment, but the thermal efficiency is insufficient. This results from an installation of small injection nozzle diameter. Then the nozzle sizes and compression ratios are selected to improve the thermal efficiency by the test.

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A supercharging system comprising of a mechanical supercharger and a turbo charger was investigated with experimental and numerical analysis in a diesel engine for use in a commercial vehicle. The frictional losses of the mechanical supercharger were reduced by putting it together with a turbo charger. Furthermore, it was found that the fuel consumption of the vehicle could be improved by optimizing power train specifications. This was accomplished due to the increased low-end torque which was enabled by a mechanical supercharger.

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Three types of experiments of shock-tube, computation, and theoretical thought indicate a high potential of the new compression principle, which was proposed by first-author's patents and previous reports of us. The engine based on the principle essentially differs from the traditional four types of engines with piston, turbofan, ran-scram, and pulse-detonation, because the new compression principle is based on supermulti-jets colliding with pulsation. This engine makes it possible that higher compression ratios result in lower noise, lower emissions, and higher thermal efficiency. A way to generate pulsation is a new rotary plate valve, which is relatively silent. Shock tube experiments and numerical simulations on super-computers show a possibility of stable and high compression. This compression principle with supermulti-jets colliding can be used for three purposes of automobiles, aircrafts, and electric power plants. To say more on the possibility for near future automobiles, this compression principle is also effective for preventing the knocking phenomenon as the critical problem for small turbo-charged engines and also for realizing higher-power Atkinson cycle, extremely lean burning in direct injection engines, and silent auto-ignition engines of gasoline.

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Optical engine indication synchronized with standard pressure recording allows a much more detailed characterization of the in-cylinder charge formation process. Information on the gas composition and temperature of the in-cylinder charge at a given crank angle is of upmost importance to improve engine performance. A fiber optical probe integrated in a spark plug or glow plug allows a real-time, crank angle resolved recording of the entire mixture formation process over hundreds of subsequent individual cycles. The in-cylinder probe measures simultaneously fuel and exhaust gas density as well as the gas temperature during the in-cylinder charge formation process. The measurement principle of optical engine indication is based on absorption spectroscopy of water, carbon dioxide and hydrocarbon fuel molecules. The measurement takes place in unmodified gasoline or diesel engines under real fuel conditions. The carbon dioxide detection reveals information about the internal Exhaust Gas Recirculation (EGR) rate for each individual cycle and cylinder, while the local air/fuel ratio measurement identifies misfire behavior during cold start. The knowledge of the gas temperature profile during the compression stroke provides important feedback for engine optimization like the HCCI pre-combustion temperature analysis.

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An experimental investigation was performed to analyze the effects of EGR rate and turbulence flows on the combustion and flame propagation characteristics of methane (CH_4) - air gaseous mixtures in a constant-volume optically accessible combustion vessel (CV). In this study, combustion pressure data is analyzed in detail for ignition delay and combustion duration, with high-speed schlieren imaging analyzed for flame propagation characteristics. Experimental results showed that the peak combustion pressure decreased as the EGR rate increased. The slope of the pressure rise is lower with a higher EGR rate, resulting in a longer time to reach the maximum pressure compared to 0% EGR. The combustion performance of 20% EGR revealed a near misfire phenomenon, meaning it is difficult for the 20% EGR gas to achieve stable combustion performance under a quiescent condition. The rate of growth of the flame kernel decreased with an increase in EGR, and hence the flame size of 20% EGR case was the smallest at every given time. The influence of turbulent flow on the combustion characteristics showed that the combustion duration was significantly shortened for all EGR rates with compared to the results of quiescent combustion cases.

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Homogeneous Charge Compression Ignition (HCCI) engine has the potential to achieve lower NOx and PM emissions with high thermal efficiency. However the operation region is limited by knocking. Combustion phasing retard is one of the methods to avoid knocking. However, excessive retard happen unstable combustion. This study explores how the cycle-by-cycle variations of HCCI engine are affected by charge constituents, which includes air, fuel, cold EGR and re-breathing EGR (hot EGR). The engine was fueled with Dimethyle Ether (DME). The experiments were conducted in a single-cylinder HCCI engine equipped with two-stage exhaust cam for re-breathing EGR and four throttle valves. In this study, it is important to detect each gas volume and temperature every cycle because combustion phasing depends on the in-cylinder mass averaged temperature. Therefore the engine included fast-response sheath thermo couples located near the exhaust valve to quickly measure the exhaust gas temperature and re-breathing EGR temperature and fast-response laminar flow meter to measure cycle-to-cycle intake air and cold EGR flow rate.

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High fuel-injection pressures and high EGR rates are strategies for reducing soot and NOx for diesel engines. These two emission-reduction methods are interdependent and tradeoffs must be evaluated. High fuel-injection pressure results in smaller soot particles, which lowers mass-based soot emission. High EGR rates increase the carbon content in the cylinder charge, which tends to enhance soot precursors formation during combustion. Smaller soot particles with a higher number density within the EGR gas favor formation of thermophoretic deposit in the EGR cooler. Increased deposit thickness on the heat transfer surfaces leads to decrease in the effectiveness and increase in the flow resistance of the EGR cooler. Consequently, deterioration in the EGR-cooler performance as a result of cooler fouling has a significant impact on engine-out NOx emissions. This study reviews the physics for the EGR cooler fouling process, characteristics of the soot deposit in the EGR cooler. Interdependence of the emission-reduction methods and their impacts on the EGR cooler fouling, and characterization of the performance of fouled EGR coolers are also discussed.

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The downsized boosted spark-ignition direct-injection (SIDI) engine is a viable technology for improving vehicle fuel economy. However, higher soot levels associated with operating the engine at significantly higher loads provide additional challenges for meeting future stringent emission regulations. In this study, we investigate the effects of exhaust gas recirculation (EGR) on soot emission levels for a 2.0 L boosted SIDI engine. Three higher load conditions (1000 rpm 210 Nm, 1500 rpm 260 Nm, and 2000 rpm 250 Nm) are examined to characterize soot emission levels with increasing EGR ratio up to 20%. An increase in EGR level provides lower soot emission levels. At 1500 rpm and 260 Nm, for example, soot emissions are reduced by nearly 50% with approximately 20% cooled EGR. Two factors are considered as primary contributors toward the reduced soot emissions with EGR: 1) lower spray penetration and reduced wall wetting, 2) lower combustion temperature within localized rich fuel pockets and within pool fire regions that may occur on piston and cylinder wall surfaces.

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Recently, NOx and PM emissions of diesel engine are regarded as a source of air pollution. And there is a global trend to enforce more stringent regulations on these exhaust gas. Therefore, several technologies have been progressively introduced in the last few decades for the reduction of NOx and PM emissions. The goal of this paper is to investigate the effect of intake air temperature on exhaust emissions in a HSDI diesel engine. This paper focuses on simultaneous reduction of NOx and PM emissions in the low intake air temperature. Experimental investigations were carried out on a 2.9L common-rail direct injection diesel engine equipped with HP (high pressure) EGR line. The experiment was conducted for one operating point, engine speed 1400rpm and IMEP 4bar, while intake air temperature was varied. Intake air temperature was controlled by intercooler and EGR cooler which were adjusted by separate cooling loop. As a result of this experiment, the decrease of intake air temperature reduced the NOx and PM emissions simultaneously through the decrease of mean temperature in cylinder and the increase of premixed period, respectively. Moreover, when intake air temperature was reduced, indicated specific fuel consumption (ISFC) was improved, due to increase of density of intake air entrained in the cylinder. On the other hand, HC and CO emissions were increased while temperature of intake air decreased. In addition, at a given intake condition, the effects of injection strategies on emissions were analyzed.

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Low pressure loop (LPL) EGR systems are effective means of simultaneously reducing the NOx emissions and fuel consumption of diesel engines. Further lower emission levels can be achieved by adopting a system that combines LPL EGR with a NOx storage and reduction (NSR) catalyst. However, this combined system has to overcome the issue of combustion fluctuations resulting from changes in the air-fuel ratio due to EGR gas recirculation from rich operating conditions. The aim of this research was to reduce combustion fluctuations by developing LPL EGR control logic. In order to control the combustion fluctuations caused by LPL EGR, it is necessary to estimate the recirculation time. First, recirculation delay was investigated, and a model was developed. A good correlation was found between actual measurements and the recirculation delay estimated by the model. Next, the control logic for LPL EGR was studied. The recirculation gas under rich operating conditions was detected by an air-fuel ratio sensor to examine a method of controlling the EGR valve in accordance with the timing for the rich gas to actually reach the EGR valve. Thus, fluctuations in torque and combustion noise were improved.

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A software framework for the construction of detailed kinetic mechanisms of combustion for versatile fuel components and mixtures named KUCRS (knowledge-basing utilities for complex reaction systems) has been developed and its structure and essential features are described. Its major purpose is to automate the routine but complex tasks for the construction, improvement and maintenance of large chemical kinetic mechanisms for hydrocarbon combustion by knowledge- and rule-based methods. It is comprised of "chemgen" (reaction macro processor), "thermgen" and "trangen" (thermodynamic and transport data generators), "combust" (main mechanism generator) and interface tools. The system features classes (program units) for the identification of chemical species by unique internal representation which takes into account the electronic structures of resonance stabilized radicals, for the administration of names and status of chemical species, as well as for the detection of duplicated reactions and dead-end species. The rate rules are defined in external text files and can be revised by mechanism developers without modifying the source code. It generates kinetic mechanism, thermodynamic and transport data compliant with Chemkin-II software and it can import/export chemical species in SMILES representation. Current version of the software can generate oxidation mechanisms for non-cyclic and mono-cyclic alkanes and non-cyclic alkenes (mono-ens) and alcohols, as well as for any mixtures consisting of any number of supported components. For multiple component fuels, it also generates cross reactions important in the low temperature oxidation.

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When the initial temperature is low, oxidation process of alkanes with the carbon number higher than three is characterized by the LTO, low temperature oxidation process. This process is controlled by RO_2 Chemistry and H_2O_2 Chemistry (Route 1). When the initial temperature is higher than T_<LTO-end>, LTO end temperature, oxidation proceeds skipping the LTO process. In such conditions, reaction proceeds by the scission of the alkyl radical, generating alkene and smaller alkyl radical (Route 2). When the initial temperature is extremely high, direct decomposition of alkane controls the reaction process (Route 3). The rate determining process of Route 1 is the β scission of ketohydroperoxides generated by RH→R→ROO→QOOH→OOQOOH→ Ket(Ald)OOH, the rate determining process of Route 2 is the dissociation of H_2O_2, H_2O_2→OH+OH. The rate determining process of Route3 is the branching chain reaction H+O_2→OH+O.

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The effect of the initial pressure and the initial fuel, O_2 and N_2 concentrations on a relationship between the initial temperature and the ignition delay in a constant-volume vessel was discussed using a detailed chemical kinetic model of n-heptane generated by KUCRS. When the initial temperature increases, the branch of C_7H_<14>OOH removal into the second O_2 addition and the decomposition is more sensitive to the O_2 concentration, and thus, the LTO preparation phase is more affected by the O_2 concentration. When the O_2 concentration increases, due to the activation of the second O_2 addition to C_7H_<14>OOH and the less accumulation of intermediates, the LTO end temperature increases. The TIP phase is controlled by the rate of H_2O_2 (+ M) = OH + OH (+ M). When the pressure increases, the rate of this reaction increases by the dependence order of about 2, and due to the proportional increase in the whole gas concentration, the ignition delay shortens by the dependence order of about 1 in the blue-flame dominant region.

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A correlation of ignition delay time with research octane number (RON) and critical compression ratio (CCR) has been investigated by using detailed chemical kinetic models of 36 alkanes for further understandings of the autoignition phenomenon in engine related to the chemical structure of fuel molecule. All the ignition delay times of stoichiometric alkane/air mixtures are equal at each initial temperature and pressure corresponding to the top dead centre (TDC) condition of CCR. From the comparisons of temperature and species profile in engine and constant volume reactor calculation, it was confirmed that the reactions before TDC is insensitive to ignition timing. Thus, RON reflects only the reaction kinetics of TDC temperature and pressure. This facts would lead to the straightforward estimation of RON.

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Intermediate species formed in the low temperature heat release (LTR) of autoignition were evaluated in test engines by crank angle resolved in-cylinder sampling and exhaust gas analysis with FT-IR at hot ignition suppressed conditions. PRF (iso-octane/n-heptane) and NTF (toluene/n-heptane) were used as the fuels. The LTR fuel consumption decreases with increasing iso-octane content in PRF, whereas the effect of toluene in NTF is weaker. Formaldehyde generation yield increases with increasing iso-octane content in PRF but the opposite trend was found in NTF. The chain reaction mechanism of LTR accounts for the observations; i.e., the chain carrier OH reproduced by n-heptane is consumed by iso-octane, toluene and intermediates such as formaldehyde. Reaction pathways for product species characteristic to each fuel component are also discussed.

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In order to meet challenging efficiency and emission target, modern engine design is more likely to involve mixed-mode of combustion as well as multiple fuels. In order to accurately predict the process of such combustion in CFD, detailed chemistry based modelling approach is required. This paper introduces the concept of Progress Variable Library Model for Multi-fuel (PVM-MF) Combustion. PVM-MF is designed to model mixed-mode of combustion with multiple fuels while keeping the computational cost low due to the use of the pre-computed libraries. The paper summarizes the application of PVM-MF in four typical modes of engine combustion, namely premixed, non-premixed, compression ignition and mixed mode. The implementation of this model in STAR-CD CFD code is described. To demonstrate the application of the model some IC engine cases are also presented.

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A two-dimensional direct numerical simulation (DNS) was applied to investigate the autoignition process of an n-heptane/air mixture. The diffusion of intermediate species was studied in terms of the influence on the ignition delay period and the chemical reaction process. A simplified reaction mechanism was used in this study. The influence of turbulence was investigated by comparing the results of a zero-dimensional simulation and two-dimensional direct simulation of a non-turbulence condition. It was found that the ignition delay period was strongly affected by the different diffusion rates of intermediate species. It was shown that the outflow of OH radicals having a larger diffusion coefficient reduces the reaction rate at the high temperature point. In contrast, the reaction rate was enhanced by the influx of OH radicals at the low temperature point.

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In this study, the findings in which the low temperature plasma technology was applied to the autoignition promotion and control at autoignition timing of the HCCI (Homogeneous Charge Compression Ignition) combustion were reported. The low temperature plasma igniter of a barrier discharge model (Barrier Discharge Igniter; BDI) with high frequency voltage (15 kHz) was provided in the top center of the combustion chamber, and the autoignition characteristics of the HCCI combustion by the low temperature plasma assistance was investigated by using single-cylinder gasoline engine. HCCI combustion with compression ratio of CR=15 was achieved by rising the intake air temperature. The combustion characteristics of baseline HCCI without discharge assistance, spark assisted HCCI, and BDI assisted HCCI were compared. The difference of combustion characteristics when changing the discharge onset timing of BDI was considered. And the mechanism of autoignition promotion for HCCI by low temperature plasma was considered.

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We aimed at the development of the powerful ignition system (active ignition) that achieves highly effective combustion. In order to achieve the stabilization of the initial combustion, we had been studying the generation of active species mass, volumetric ignition and a long pulse duration discharge. In this study, we developed the ignition system without a large-scale structural change from a conventional engine. The active ignition system consists of a primary coil (ignition coil) of standard spark discharge, and a secondary coil of high frequency supply. Plasma is generable by emphasizing sparks with high frequency voltage. By applying a high frequency voltage, the spark discharge can increase the speed and the number of collisions. Plasma and free radicals are produced by this phenomenon. In order to compare the effect of ignition, the constant volume combustion chamber that can give a flow was used and took a high-speed video using Schlieren photography. In this study, we report that the improvement of combustion in the engine by using a new ignition system applied HF electric field.

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This study developed an innovative microwave plasma combustion system to improve fuel economy and achieve higher efficiency for spark ignition (SI) engines. Microwave plasma technology was combined with an active ignition system, which generates plasma by applying a high-frequency voltage to the standard spark discharge. A standard ignition coil was used. The high-frequency voltage was applied at frequencies ranging from kHz to MHz; the voltage exceeded the inductive discharge voltage and was less than the capacitive discharge voltage. The high-frequency voltage was applied just after the SI timing of the standard spark system, and the pulse width was changeable. A magnetron supplied microwaves to the cylinder through a waveguide, co axial cable, mixer unit, and center electrode of a non-resister spark plug. The mixer unit functioned as an isolator to prevent adverse current due to the high frequency and microwave oscillation. Engine modifications were not required for this ignition system. During the active ignition and microwave operating cycles, the heat release was stable and the indicated mean effective pressure (IMEP) fluctuation was relatively low. Without microwave oscillation, the initial combustion period became unstable and there were some partial burn cycles. The initial combustion period and IMEP were strongly correlated. Therefore, the stable, short initial combustion period led to a high IMEP and less combustion fluctuation. To optimize the microwave oscillation timing, the effect of the microwave timing on the torque was investigated. This showed that the torque curve had two peaks when plotted against the timing of the microwave oscillation: the first peak was related to the microwave plasma generation, which utilized the high-performance ignition as a source of the plasma, and the second peak was outside the range of the high-performance ignition timing. This means that the microwaves improved the initial flame development, not the ignition, suggesting the possibility of further fuel economy improvement by enhancing flame propagation under ultra-lean or high emission gas recirculation (EGR) conditions.

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The aim of this study is to demonstrate a novel combustion system in which autoignition is induced by spark discharge into a pre-mixture formed during a long ignition delay time in a low compression ratio direct injection diesel engine. An experiment is conducted to investigate the potential of spark discharge on the autoignition process by changing the spark timing, injection timing, equivalence ratio, and fuel amount. The fuel used is lauric methyl ester (LaME), which is a fatty acid methyl ester (FAME) that has relatively high volatility and high ignition quality. The results of our study show that with a volumetric efficiency of 34%, spark-induced compression ignition (SICI) combustion is observed. In this study, the ignition delay time is advanced for about 5 deg. CA, and the ignition timing is controlled by spark timing within 5 deg. CA. In the paper, we also discuss the applicability of starting performance, which is a major problem in low compression ratio diesel engines due to lower temperature at the end of the compression stroke, compared with high compression ratio diesel engines

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In this contribution, an initial investigation of the ignition behavior of large two-stroke marine diesel sprays has been performed. At engine-like conditions, the OH radical was traced with an intensified high speed camera and a sophisticated optical setup. A series of spectroscopic measurements showed, however, that the soot incandescence strongly contributes to the UV signal, superimposing with or even masking the chemiluminescence of the OH radical. As the combustion of typical fuels used in large two-stroke engines involves the formation of non-negligible amounts of soot, the signal is almost omnipresent during the oxidation process. A differentiation between the UV-light emitted by the OH radical and the UV-light emitted by soot incandescence is only possible when both signals are measured separately. Therefore, a second high speed camera recorded the light coming from soot incandescence. In addition, it recorded the background illuminated spray plume to make an exact positioning of the OH* signal relative to the spray possible. A comparison of the two images then allowed the differentiation between the two light sources. In a first measurement series, which included a temperature variation, ignition delay, ignition location and flame lift-off have been measured. The results are in accordance with literature, as they show a dramatic decrease in ignition delay towards higher gas temperature. On the other hand the standard deviation increases towards lower gas temperatures. The ignition location and lift-off showed similar behavior: Lower gas temperature corresponds to an increase of the distance between ignition location/lift-off and nozzle orifice along with increased standard deviation. It could be shown that the applied technique works for the investigation of large marine diesel engine combustion systems.

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The marine industry is faced with new tough emission regulations. Experimental results are reported on gasoil and LCO (light cycle oil) water-in-fuel emulsions, on effects of nitrogen enriched charge air and on the combination of the two technologies. The Two Color Method is applied and results compared with the Back Diffused Laser method, while emissions and rates of heat release are discussed. The potential of using emulsions to improve the combustion process, drastically reduce soot and potentially to lower NO_x emissions is demonstrated, while the combination with nitrogen enriched charge air to drastically reduce NO_x emission leads to a promising solution by combining advantages.

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The nano air-bubbles mixed into gas oil are used for the energy saving and environmental load reduction of diesel engine. The nano air-bubbles were mixed into the fuel line continually by a super miniature ejector-type mixer (outer diameter:20mm, length:34mm) which can make nano and micro sizes. After the micro air-bubbles were separated with the nano air-bubbles in a mixing tank, diesel engine performance test with a common-rail injection system was experimented. The results showed that 3% reduction in break means specific fuel consumption, 1% rise in charging efficiency and a slight reduction in the density of exhaust smoke etc. These were caused by mixing the nano air-bubbles into gas oil. It is confirmed that the nano air-bubbles had advanced and activated combustion by a physical and chemical action.

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The formation of the fan-shaped spray through the new-type nozzle named V-type intersecting hole nozzles (IH nozzle) was proven by means of visualization. The spray characteristics including spray angle and spray tip penetration were studied by the comparison of two IH nozzles with different intersecting angles and a single hole nozzle (SH nozzle) in variable boundary conditions. Experimental results showed the spray angles in X and Y directions of the IH nozzles, as well as the spray tip penetration, were adjusted by the intersecting angle of the sub-holes inside the IH nozzles. A concept named spray volume enhancement ratio, δ_<SVER>, was also used in order to qualitatively estimate the injector performance as far as the end fuel mixture. In addition, numerical simulation was carried out to analyze the effects of the intersecting angle on the velocity characteristics, as well as cavitation in AVL-FIRE environment.

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The present study is carried out on a light duty direct-injected diesel engine with Bowditch type optical access. Planar laser induced Mie scattering images, recorded at 20 kHz, are used to follow the evolution over time of the liquid phase of the jets. Different fuel injection strategies for diesel particulate filter regeneration are investigated. An additional focus is put on the fuel effects. The Swedish standard diesel fuel MK1 and a reference fuel free of Rapeseed Methyl Ester (RME) are tested. A Biodiesel fuel composed of 10% of RME is also tested in order to evaluate the impact of this blend on the liquid spray penetration length.

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Diesel engines have high thermal efficiency, but suffer from the problem of relatively high emissions of NOx and particulate matter. The authors have shown that NOx is mostly generated at the flame tip region where mixing strength decrease significantly and maintains high temperatures for longer times than other regions. Based on this assumption, the authors proposed a combustion concept to reduce NOx by introducing high turbulence in the combustion chamber during the combustion period. The present paper reports simulations of the turbulence intensity and NOx reduction for an engine, which is designed to generate a strong jet from a special cell. The cell, which is termed CCD in the paper, is added to a direct injection diesel engine, and a small amount of fuel is injected into the cell to create the strong jet entering the main chamber. The numerical simulations showed that NOx increased significantly by the jet from the cell, the opposite of the expected result. However it was shown that a significant NOx reduction was obtained when the jet was injected in the same direction as the fuel injection, showing the viability of the concept.

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In order to achieve the clean exhaust emissions and the high fuel efficiency in a diesel engine, it is necessary to optimize the mixture formation and the combustion processes. A combustion chamber shape is one of the dominant factor among the many factors in determining the combustion characteristic. In this study, a new concept of combustion chamber shape, an Egg-shape combustion chamber was proposed. For the first step, to examine its effectiveness on the mixture formation, the combustion process and the exhaust emissions, numerical simulations by Computational Fluid Dynamics were carried out under the engine operating condition. Secondly, to clarify the behavior of fuel spray and the combustion characteristics, the experimental measurements by means of Laser Absorption Scattering method and Two-color method were carried out under the conditions of wall-impinging spray and combustion with constant-volume vessel. Through the numerical simulations and the experimental measurements, it was clarified that Egg-shape combustion chamber concept is very effective to enhance the in-cylinder gas mixing and to reduce the exhaust emissions. Finally, this Egg-shape combustion chamber concept was proven as effective in improving the exhaust emissions and the fuel efficiency by the engine experiments.

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In order to gain a better understanding of the soot formation mechanism involved in the combustion process of hydrocarbon fuels, laminar premixed n-heptane flames with different equivalence ratios (1.20, 1.60 and 1.80) are studied by using synchrotron photoionization and molecular-beam mass spectrometry (PI-MBMS) techniques at low pressure(30Torr). To isolate the influence from flame temperature, the composition of unburned mixtures is adjusted such that the temperature profiles are approximately equivalent. Mole fraction profiles of major and intermediate species were derived and compared among different flames. Parallel modeling study based on a modified mechanism is conducted. The predicted mole fraction profiles of concerned species agree reasonably well with experimental measurements. The results show that, as equivalence ratio increases, the equilibrium mole fractions of H_2O and CO_2 decrease while those of H_2 and CO increase, and the concentrations of benzene and toluene and those of C_2-C_5 hydrocarbon intermediates increase apparently. The reaction flux analysis indicates that the self-recombination of propargyl radical (C_3H_3) and the cross reaction between C_3H_3 and allyl radical (a-C_3H_5) are the dominant pathway leading from small aliphatics to C_6H_6. The consumption of C_6H_6 is primarily resulted from the attack by OH and H radicals. The larger amount of C_6H_6 formed in richer flames should be attributed mainly to the higher concentrations of benzene precursors. In addition, the weakening influence of the OH-attack and O-attack reaction tends to slow down the consumption of C_6H_6, which also contributes to the higher C_6H_6 concentration in the richer flames.

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An LDV system was employed to measure three components of velocity at a mid-flame point on the centerline of a propane-air flame of equivalence ratio 1.10 on a 26 mm-diameter Bunsen burner with fully developed turbulent pipe flow upstream at a Reynolds number of 6700. The LDV measurement volume was 1 mm below the leading electrode of a four-element electrostatic probe that provided the velocity and direction of motion of flamelets in the turbulent flame brush. It was found to be possible, during each flamelet passage, to rotate the coordinate system about a vertical axis so that the flamelet and all gas velocity vectors remained very nearly in the same vertical plane, thereby implying locally nearly two-dimensional motion, insofar as the influence of the gas expansion on the gas velocity is concerned. In the local plane of motion, the observed changes in gas velocity caused by flamelet passage exhibited a downward component for upward moving flamelets with the fresh mixture above the burnt gas and an upward component for upward moving flamelets with the burnt gas above the fresh mixture, consistent with the expected gas expansion through the flamelet. Moreover, within the accuracy of the LDV measurements, profiles of changes of the component of gas velocity normal to the flamelet agreed with velocity profiles calculated for steady, planar, unstretched, premixed laminar flames. These results indicate relatively little distortion of laminar flamelet structures in the turbulent flame brush at these turbulent intensities of about 5%.

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