It was shown in a theoretical study that a unique relation exists between the emission intensity ratio of the C_2 Swan Bands (515, 470nm bands) and the flame temperature in hydrocarbon/air premixed flames. It implies that the flame temperature of hydrocarbon/air premixed flames can be estimated by measuring emissions of the C_2 Swan Bands. However, emissions of the C_2 Swan Bands are feeble especially in lean hydrocarbon/air flames. In order to detect feeble emissions of the C_2 Swan Bands in lean hydrocarbon/air flames, a spectrometer, composed of dichroic mirrors, band pass filters, photo-multiplier tubes and an I/V amplifier has been newly developed in our laboratory. Use of the newly developed spectrometer together with Cassegrain optics enables to detect feeble emissions of the C_2 Swan Bands with high spatial resolution on the order of 0.1mm. In order to explore the behavior of the near extinction flamelet in turbulent premixed flames, the relation between the emission intensity ratio of 515/470nm band of C_2 (C_2*(0,0)/C_2*(1,0)) and the flame temperature for various strain rates has been sought in both unstrained and strained flames by using a rectangular nozzle burner and a counter-flow burner, respectively. The relation between C_2*(0,0)/C_2*(1,0) and the flame temperature obtained from both unstrained and strained propane/air premixed flames. For unstrained flames, as the equivalence ratio of the mixture decreases in the lean side, C_2*(0,0)/C_2*(1,0) and the flame temperature decrease. A unique relation is experimentally found to exist between C_2*(0,0)/C_2*(1,0) and the flame temperature. For strained flames, as the strain rate increases with the equivalence ratio of the mixture is constant, the flame temperature decreases, and C_2*(0,0)/C_2*(1,0) decreases slightly. It can be concluded that if the equivalence ratio of the mixture is known, the flame temperature of strained flames can be estimated.

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Non-intrusive flow measurements are useful for the understanding of physical processes central to engine combustion and emission performance, such as fuel-air mixing. In the present work, a test rig with maximum optical access is designed and fabricated to study the incylinder flow due to reciprocating piston during compression using particle image velocimetry (PIV) and proper orthogonal decomposition (POD), a technique for investigating turbulent flows. Very few investigations of the incylinder flow using the PIV-POD combination are reported in literature. The effects of the piston configuration and the piston position on the incylinder flow are investigated, for two piston configurations, viz., flat piston, and spherical bowl, six piston positions, from the bottom dead centre (BDC) to 150° after BDC, in steps of 30°. PIV measurements are carried out in the vertical plane passing through ports at 600 rpm crank speed. The ensemble-averaged velocity fields obtained from PIV reveal a large scale rotation particularly in the early part of the compression stroke, i.e., from BDC to 90° after BDC (aBDC). In the later part of compression, the flow is observed to be directed towards the cylinder head. POD is applied to the measured instantaneous velocity to study the incylinder turbulent flow. The POD modes show the flow fluctuations due to the effect of turbulence and cycle-to-cycle variations. For the spherical bowl case at 150° aBDC, the share of the fluctuation kinetic energy in the second and higher POD modes is higher than that (a) at any other piston position (b) in the case of flat piston. Thus, the POD analysis of instantaneous velocity measured using PIV, indicates that a spherical bowl is a better choice in terms of turbulence production compared to a flat piston, for use in engines.

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In this work, the pathways and challenges for enabling the clean and efficient combustion are first identified with extensive engine tests on a high compression ratio single-cylinder diesel engine. The engine load and emission trade-offs are analyzed for different fuel injection strategies, intake boost, injection pressure and exhaust gas recirculation. The identified challenges are then analyzed to define the requisite control strategies for improving the stability and combustion efficiency of such clean combustion processes. Moreover, the critical issue of switching in multi-mode combustion on-the-fly is also addressed and empirically demonstrated for the seamless transition from the single-injection to multi-injection modes in 3 consecutive engine cycles without leaving low temperature combustion. To further demonstrate the robustness of the control system, the use of ethanol in a dual-fuel configuration with a diesel pilot-injection is demonstrated to extend the load limit of clean combustion. This research intends to advance the control methodologies for application of the clean combustion modes over the engine operating regime.

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As compared with the conventional diesel combustion, Premixed Compression Ignition (PCI) combustion has an opportunity to achieve low fuel consumption and clean exhaust gas simultaneously. However, to improve the stability of fuel consumption, exhaust gas, and combustion noise, it is necessary to control ignition timing appropriately in PCI combustion. We therefore conducted a study to develop a new prediction model to control ignition timing. In this model, an empirical equation of Arrhenius expression including some sub-models and Livengood-Wu integral were applied to consider the in-cylinder condition of a mixture formed by fuel injection. The model constants were determined based on the experimental results obtained by Design of Experiments (DOE) so that sufficient prediction accuracy could be achieved for transient operating condition. By using a mass-produced Engine Control Unit (ECU) employing feed-forward control logic based on this model, we confirmed that the ignition timing in the transient operating mode could be controlled rather well by reflecting a predicted ignition delay period to fuel injection timing. With the controllability of ignition timing, the robustness of engine performances in terms of fuel consumption, exhaust gas and combustion noise could be improved with PCI combustion.

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The simultaneous reduction of NOx and PM is an urgent challenge for diesel emissions. In this paper, di-methyl ether (DME) was used as a NOx deoxidizer in a selective catalytic reduction (SCR) after-treatment system. With 574 grams of 2-3 mm diameter pellets of Ag(1wt%)-γAl_2O_3 in the cylindrical vessel of the SCR, the emissions and temperatures were sampled and measured at four different points in the after-treatment system. The diesel engine was operated under four test conditions, varying the BMEP, the DME/NOx, and the intake oxygen contents, and the NOx conversion ratio was investigated based on the activation temperature of the catalyst, the NO-NO_2 conversion ratio and the chemical species produced with DME. A 300-400℃ activation temperature of the SCR and NO-NO_2 conversion are the important factors in the NOx conversion. Further, it was found that the CH_4 produced in the decomposition of DME acts as a reduction agent for the NOx conversion.

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Recently, Urea-SCR system has been used for reducing NOx emission from diesel engine. In the Urea-SCR system, aqueous urea is injected into the exhaust gas flow and it evaporates and decomposed to NH_3. It is necessary to clarify thermal decomposition behavior of urea in high temperature atmosphere to improve the DeNOx performance of Urea-SCR system. In this study, thermal decomposition behavior of urea in heating processes was investigated experimentally. Solid urea or 32.5% urea aqueous solution was decomposed in a temperature controlled vessel with a constant heating rate. Mass reduction of the sample with decomposition was measured with a balance. As for the thermal decomposition behavior of solid urea, it was shown that the remained mass in higher heating rate was higher than that in lower heating rate at the same temperature in the vessel. From the temperature measurement of the sample, it was found that the thermal decomposition which was endothermic reaction occurred rapidly in the higher heating rate, and therefore the increase of sample temperature became slower than the heating rate. This delay of sample heating resulted in the higher remained mass at the same temperature in the vessel. In this study, moreover, effect of zeolite on the decomposition behavior was examined. Some kinds of zeolite are used as a catalyst in Urea-SCR system. In the thermal decompositions of urea with zeolite, several kinds of zeolite were tested. The zeolite powder was mixed with the solid urea or urea aqueous solution. As the result, it was found that some kinds of zeolite could effectively promote thermal decomposition of urea.

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In order to examine the effects of aromatic addition to Fischer-Tropsch Diesel (FTD) fuel on formation and growth processes of PAHs and soot particles in its spray flame, small amount of naphthalene (20 to 13000 ppm) was added to the FTD fuel and the formation and growth processes of PAHs and soot particles in its spray flame were investigated via high-speed laser shadowgraphy, 2-color method and Excitation-Emission Matrix (EEM) technique. The experiments were conducted using an optically accessible constant volume combustion vessel at 1000K and 2.7MPa under EGR-like 15% O_2 condition. The experimental results indicated that naphthalene addition does not affect on ignition delay and heat release rate within the investigated concentration range. The added naphthalene promoted formation and growth of PAHs in the spray flame, advanced soot particle formation in the flame and increased apparent flame temperature measured via 2-color method by up to 100K. The apparent temperature increase is likely due to accelerated soot oxidation in the flame periphery, while the reason for the accelerated oxidation is not clear at this moment. The resulting soot production in the spray flame did not show significant difference due to naphthalene addition, likely because the soot formation promoted by naphthalene addition and the accelerated soot oxidation cancelled out.

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Recent years have already seen tighter regulation on harmful substances such as NOx, CO, and particles. Considering the above situation, it is important to monitor controlling factors of engine systems in order to improve efficiencies of their operations. In car engines an increasing concern in environmental issues such as air pollution, global warming and petroleum depletion has helped drive researches into various ways. Laser diagnostics has been applied to measure species concentration in the actual industrial fields. However there are several challenges to proceed in applying laser diagnostics to practical application. Especially stability of the measurement system is one of the most difficult issues. The purpose of this research is the development of a prompt measurement technique which can be applicable to various engine conditions. The tunable diode laser absorption spectroscopy(TDLAS) using the hollow fiber has been developed to satisfy above requirements. By using a hollow fiber, misalignment of an optical axis and vulnerability of measurement environment such as vibration can be greatly reduced with sensitive and fast response features. It was demonstrated that this method can be applicable to measure gas compositions in engine exhaust with a range of millisecond response time. A sensitive method using tunable UV diode laser absorption spectroscopy was also discussed to detect NOx in exhausts.

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CO emission sources in diesel combustion with multiple injections are analyzed by using in-cylinder CO imaging and 3-D numerical simulation. For the in-cylinder CO imaging, a two-photon excitation LIF was applied. While overlapping of the blue color component of the luminous flame (emitted by the soot particles) over the weak CO fluorescence became as a serious problem, it was solved by optimizing the viewing direction. A comparison of the CO distribution results as obtained by CO-LIF imaging and CFD simulation shows good agreement on the location of the dense CO gas clouds. The major source of CO emissions under low-load conditions is the over-diffusion of the pilot sprays. A large amount of CO, formed from the pilot flame, is emitted without being oxidized by the high temperature main flame. In contrast, under high-load conditions, the major source is the fuel rich region of the flame front because of the low O_2 concentration.

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Most of the recent clean diesel engines are generally equipped with an exhaust recirculation (EGR) technology in order to meet the strict criteria of NOx emission regulations. In the field of emission control, accurate and fast transient EGR ratio operation is becoming very critical. In this study, a transient EGR analyzer has been developed and evaluated with a conventional exhaust gas analyzer system to confirm the advantage of the transient EGR analyzer. As a consequence, the faster response has been observed from the transient EGR analyzer without significant transient error under transient test cycles. The EGR ratio measured by the transient EGR analyzer followed up the EGR valve operation well. These results show the advantages of the transient EGR analyzer for measuring EGR ratio under the transient cycle. Additionally, a simulation of the optimum response time was conducted. The gas transition time of the engine EGR system was simulated by z-transformation using the response time of measured actual exhaust gas. As a result, the optimum response time required to the EGR measurement system was estimated for the test engine.

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Methyl oleate is a long chain methyl ester and a major constituent of rapeseed-oil derived biodiesel. A detailed mechanism for its combustion was recently developed by Westbrook and co-workers. This master mechanism involves 5037 species and 19990 reactions, which makes it too complex for direct use in computational fluid dynamics. In the present work, various mechanism reduction methods were used to derive a skeletal biodiesel combustion mechanism that retains the key properties of the master mechanism (auto-ignition behavior, fuel conversion rate) and generates similar concentration profiles for intermediate species. This skeletal mechanism containing only 442 species was applied to study the methyl oleate oxidation in an opposed-flow diffusion flame and the combustion phasing under the diesel engine conditions. The skeletal mechanism was proved to be the efficient and accurate representation of actual biodiesel combustion and emissions formation.

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Total particulate number, size, and morphology were analyzed for several biofuel blends fired in a gasoline direct injection engine. The particle sampling was taken at several common operating conditions using a Scanning Mobility Particle Sizer (SMPS) unit and a thermophoretic sampling device. The fuels tested were gasoline, E10, E85, and iso-butanol-16 (iB16) and the test points were for 25%, 50%, and 75% loads at 2,000 rpm as well as idling. Exhaust gas recirculation (EGR) levels or fuel injection parameters were not changed from the manufacturer's setup. There were significant differences in the levels of particulate number produced for the fuels and for the different load/speed combinations. E85 produced significantly lower particulate levels than did any of the other fuels tested. The E10 and iB16 produced higher levels than did the gasoline fuel in the entire load rage, due to the inherent thermo-physical and chemical properties of the alcohol fuels. At a 75% engine load, the particulate size measured by the SMPS increased in the order of gasoline, E10, and iB16. This trend quite agreed with the size data measured by a transmission electron microscope. The TEM observation of particle morphology showed that particle number concentrations were extremely low at 25% and 50% loads, particularly with the biofuel blends. Further detailed analysis in morphology for the biofuels revealed the nanostructures significantly different from those for the gasoline, exhibiting a lower level of graphitic structures with some amorphous structures.

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In recent years the use of computational simulation tools for combustion research has appeared as a way to reduce time and cost in engine research. These tools face important challenges due to the complexity of the composition of the hydrocarbon petroleum fuels. One of the solutions to this problem is the use of surrogate fuels, with known physical and chemical properties and combustion characteristics similar to real fuels. This paper presents experimental and modelling studies of auto-ignition for long-chain hydrocarbon fuels such as dodecane and hexadecane. Results show a very good agreement for dodecane fuel and hexadecane fuel, with small differences for the latter at lower temperatures which could be caused by the intrinsic nature of the model. These results represent as first step on the development of a surrogate diesel fuel for auto-ignition and soot modelling.

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The knowledge about fuel composition effects on the combustion behavior becomes more and more important due to strict legislative exhaust emission restrictions on the one hand and modified fuel compositions on the other hand. In diesel combustion the addition of new fuel components, such as fatty acid methyl ester and pure alkanes from the Fischer-Tropsch-synthesis, have significant effect on the thermo physical properties of the diesel fuel mixture and therefore influence the injection and the evaporation process. These processes have a strong impact on the following ignition and combustion process and therefore on the power generation, engine noise and emissions. This can be seen in gasoline and diesel injection. In the present investigation the focus was set on the ignition phase. Using a typical piezo-type diesel injector and injection pressures up to 200 MPa different diesel fuels were injected into a stationary high temperature (up to 1000 K) and high pressure (up to 10 MPa) atmosphere. By means of two different cameras the spray formation and the appearance (time and location) of premixed and diffusion controlled combustion were acquired, separately. It was found that the timing of the ignition processes (premixed and diffusion controlled combustion) was dominated by the ambient gas temperature while the location of ignition is defined by the pressure ratio between gas and fuel. The time delay between the first appearance of the lean combustion and appearance of the diffusion controlled flame was consequently also dominated by the gas temperature. At part load conditions the UV-flame appeared at 800 μs after the visible start of injection while at full load conditions the ignition delay was reduced to 250 μs. Cetane-number was not found to have big effect on ignition timing under the conditions applied. The start of combustion was found on the front or the side of the spray cone tip for all operating conditions investigated.

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Flame lift-off length in diesel spray is currently recognized as an indicator of sooting tendency during mixing-controlled combustion and is affected by fuel reactivity. This paper reports the experimental investigation of the flame lift-off length and its effects on emissions for dual-component fuels consisting of different less reactivity component. The experiments were conducted at quiescent ambient condition in a Rapid Compression and Expansion Machine. Gasoline-like components contained in dual-component fuel and ambient oxygen concentrations were set as major experimental variables. The experimental results, based on pressure analysis, burned gas analysis and imaging of luminous flame and OH chemiluminescence, show that mixing higher octane number component has lower luminous intensity indicating lower soot because of longer lift-off length and dual-component fuel achieves low soot and NO_x combustion without excessive decrease of ambient oxygen concentration.

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Due to the low volatility and high reactivity of conventional diesel fuels, the efficient combustion of a highly homogenous cylinder charge is normally limited to low loads. When the compression ratio, and thus the expansion ratio for prevalent engine designs, is substantially lowered to accommodate higher loads, the energy efficiency of the cycle is significantly reduced. In this work, with a high compression ratio of 18.2:1 kept intact on a single cylinder engine platform, the charge homogeneity is raised by adding fuels of higher volatility and lower reactivity at the intake port of the engine. The impact of port delivered gasoline has been reported by the authors previously; herein the usage of ethanol and butanol are investigated for their respective impacts on the enabling of ultra-low NOx and soot combustion at an elevated load level of 0.8 MPa IMEP. In order to attain appropriate combustion phasing with adequate burning completeness, the ratio of the port injection fuel and the direct (high pressure) injection fuel were adjusted; along with the modulation of the timing and events of the diesel pilot. The use of ethanol as a main fuel of energy supply demonstrated superior performance of clean and efficiency combustion for a load up to 1.36 MPa IMEP. Higher load operations have led to the premature auto-ignition of butanol and ethanol respectively, whilst butanol imposes the load barrier earlier than ethanol. Similar to the symptoms of most homogeneous charge engines, higher levels of total hydrocarbons and carbon monoxide emissions loom especially when excessive EGR is applied to defer the early heat-release. All the demonstrated tests are performed under the EGR and boost amounts that are considered readily achievable in an advanced production engine.

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Fuel properties, fuel injection, fuel-air mixing, and the resulting combustion processes strongly influence the functionality and performance of diesel engines. The Single-Fuel Concept (SFC) for application of JP-8 fuel to diesel engines contains potential problems for current and advanced combustion engines. In order to maximize efficiency while limiting emissions and maintaining robust combustion for these systems when using JP-8 as a fuel, fundamental spray, ignition, and combustion properties need to be thoroughly understood and characterized. Recently, surrogate fuels have been widely studied to simulate combustion characteristics of real fuels including diesel and JP-8. In this study, the combustion and polycyclic aromatic hydrocarbon (PAH) growth characteristics of JP-8 were investigated numerically through the surrogate components and results were compared with those of n-heptane under diesel in-cylinder conditions. The reaction mechanism of JP-8 surrogate fuel was modified with addition of soot chemistry from n-heptane reaction mechanism. First, closed reactor model using CHEMKIN code was used to calculate pyrene yield as PAH indicator over a wide range of temperature and equivalence ratios for both fuels. Second, the Two-Stage Lagrangian (TSL) model capable of coupling detailed chemical kinetics with a simplified jet flow field were used to simulate high-pressure spray combustion by incorporating data on mixing or entrainment of fuel/air and flame lift-off length from published experimental data. Results indicated that closed reactor simulation showed similar yields of C_2H_2, C_6H_6, and pyrene for both fuels. However, TSL model showed that PAH region was shifted to lower equivalence ratio and higher temperature compared to closed reactor simulation due to a fact that the mixing of hot air into fuel spray would result in higher core temperature.

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In the last years, increasing attention has been paid to biofuels for their potential to reduce both CO_2 emissions, considered one of the major greenhouse gas (GHG), and particulate matter mass emissions. Biodiesel can be classified in 1^<st> and 2^<nd> generation fuels. First generation biodiesel is produced from vegetable oils and animal fats through a transesterification process. The 2^<nd> generation of alternative fuel was obtained from the well-known Fischer-Tropsch synthesis process. The physical properties and chemical composition of biofuels are quite similar with respect to the conventional diesel fuel even if they can alter the combustion processes in terms of performance and emissions. In this paper, the effect of the alternative diesel fuels on particle formation and emissions was analyzed by means of optical techniques and conventional methods. The measurements were carried out on a direct injection (DI) Common Rail (CR) transparent research diesel engine. In-cylinder broadband UV-visible measurements were used to acquire information about the soot size distribution. The particulate emissions were characterized at the exhaust by means of an electrical low pressure impactor (ELPI), for the particle counting and sizing, and an opacimeter, for the smoke opacity (particulate mass concentration) measurement. The engine was fuelled with conventional diesel and two alternative fuels, chosen as representative of the first generation biofuel, namely RME, and second generation biofuel, GTL, at two engine operating conditions, 1500 rpm x 2 bar and 2000 rpm x 5 bar of BMEP, typical of New European Driving Cycle.

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It is expected that liquid fossil fuels will be replaced by gaseous fuel within twenty years, and hydrogen may be of great importance by the mid-twenty-first century. However, recently, it has been difficult to secure a hydrogen economy, which starts from the establishment of a hydrogen infrastructure and leads to production, storage, and application. A transitional strategy should be prepared, and it is believed that a kind of partial application, such as reforming hydrocarbon fuel, could be a technical bridge to a hydrogen economy. Natural gas as an energy source for transportation has the advantage of emission at low levels. However, more technical researches should be carried out to hold a dominant position of clean fuel over well-developed diesel vehicles. Hydrogen/natural gas blends (HCNG) are promising fuels for solving the problems of present natural gas vehicles. It may possibly meet reinforced emission regulation, and North America and some European countries have already begun the development of an HCNG vehicle and the supply project of an HCNG station. The HCNG research project of Korea started in 2009 for developing an HCNG bus that meets the EURO-VI standard. In order to study the performance and emission characteristics of an HCNG engine, an 11-L, heavy duty, lean burn engine was used. The level of nitrogen oxides (NO_x), the most important component of emissions, is closely related to operation strategy. Therefore, operating parameters, including excess air ratio and spark advance timing, were optimized, and other parameters for high thermal efficiency were also examined.

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Gas-jet ignition is a useful technique to extend lean combustible limit of CNG engines. Authors' previous study suggests two-stage injection; namely first injection into the engine cylinder during compression stroke and gas-jet ignition at near TDC, is effective to extend operating range from light load to heavy load. The gas-jet ignition supports ignitability of CNG and the first injection duration can easily alter total equivalence ratio. Hereafter, it is necessary to improve THC emission with high thermal efficiency at wide range of operation. This study investigated source of THC emissions formed in gas-jet combustion engine and tried to reduce THC. The study was carried out by engine test and observation of flame development in a constant volume chamber. Results show that THC emissions at light load are mainly formed by incomplete combustion at density leaner than lean limit of CNG. At high load, some THC emissions are seemed to be caused by rich combustion in clearance space of the engine chamber between piston and cylinder head. Hydrogen addition is effective to improve THC emissions more in high loads than in light loads. In high loads, hydrogen addition effectively supports initial flame development into clearance space, which causes less cyclic variation and less THC emissions.

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The present study experimentally investigated combustion characteristics of a diesel engine with hydrogen and blowby components added to the intake air. In our previous studies, the ignition delay decreased with the increase in hydrogen fraction at late diesel-fuel injection timings. However, it is difficult to auto-ignite hydrogen earlier than diesel fuel, because the auto-ignition temperature of hydrogen is higher than that of diesel fuel. There must be some factors to ignite hydrogen. We focus on reaction of blowby components as a cause of hydrogen ignition earlier than diesel-fuel ignition.

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High-pressure direct injection of the fuel into the cylinder is as a promising approach to increase the performance of gaseous fueled internal combustion engines (ICEs). Nevertheless, a direct injection (DI) strategy increases the number of degrees of freedom for optimal mixture formation. Computational Fluid Dynamics (CFD) can support this optimization process. Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model, however the numerical simulation of a high pressure gas jet is not a simple task. At high injection pressure, the gas at the nozzle exit is under-expanded and a large series of shocks occurs due to the effect of compressibility. To simulate and capture this phenomenon, grid resolution, computational time-step, discretization scheme, and turbulence model, need to be properly set. In this paper, the injection of argon at high-pressure (100 bar) in a cylindrical chamber is simulated using the CFD solver Fluent, with main focus on the characteristics of the under-expanded region. CFD results are validated through the comparison with high-definition, time-resolved measurements of gas jet mass distribution using x-ray radiography performed at the Advanced Photon Source (APS) at Argonne National Laboratory. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm and directed along the injector axis, is evaluated. An optimized computational grid is generated, with higher resolution in the under-expanded region. Results show good agreement between CFD and x-ray data. The mass distribution within the jet is well predicted by numerical simulations. The influence of turbulence model and discretization order is shown. Finally, pressure, temperature and mixing characteristics for the injected gas are illustrated in the under-expanded region.

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The established tracer laser-induced fluorescence (LIF) technique was newly adapted for the quantitative visualization of hydrogen inside an optically accessible hydrogen engine to investigate the processes of hydrogen-injection, mixture formation, ignition and combustion at motor-relevant operating points. Trimethylamine (TMA) has been seeded to the hydrogen and was thus used as a tracer for hydrogen when applying the LIF technique. End of injection (EOI) was varied at a constant speed of 2000 rpm and a load of 2 bar (IMEP) which represents typical part load condition. The results visualize the influence of EOI on the mixture formation, ignition and the beginning of combustion. The comparison of the visual results of four operating points shows how long it takes even in the case of hydrogen to get a homogeneous mixture at spark timing. Additionally, conventional engine data such as cylinder pressure, temperature, consumption, emissions etc. have been measured. Rough running engine due to uneven distribution in the region of the spark plug could be explained by single-shot images.

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The aim of this research is to explore a high efficient and low emission engine without persisting in using only a fuel. The authors are currently interested in a natural gas/diesel dual fuel engine with advanced diesel fuel injection control technology which has been developed and adopted for recent diesel vehicles. It is believed that the injection technology would be beneficial for combustion control of the dual fuel engine with high efficient and low emission. In this study, performance of the dual fuel engine was achieved to find out specific characters of the engine. Natural gas was injected into an intake port and diesel fuel was directly injected into a combustion chamber with changing amounts and injection timings of both fuels. The engine test results show that NOx emission got worse along with advancing diesel injection timings to around -40 deg. CA ATDC. However, if injection timings were advanced more, THC and NOx emissions were simultaneously decreased with an increase in indicated thermal efficiency. To deeply understand specific combustion fundamentals acquired through the engine tests, numerical CFD simulations were conducted. For the simulations, a skeletal model for natural gas/diesel dual fuel combustion was developed, and it is clarified that the simulations could reproduce similar combustion behaviors to those taken in the experiments.

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During the conventional Diesel combustion soot and nitrogen oxide are formed due to the inhomogeneous mixture process. In homogeneous or partly homogeneous operation combustion occurs in premixed and lean conditions. Therefore soot and NOx emissions are significantly reduced. In the past the last-named operating modes have been investigated mostly by experimental test-bench measurements. So far, the nonexistence of easy to use and accurate combustion models for these types of combustion regimes have prevented researchers and developers from using one-dimensional simulation tools. Therefore a phenomenological combustion model for homogeneous and partly homogeneous Diesel combustion has been developed. The low temperature combustion and the ignition delays for high temperature combustion are calculated with a global reaction model. The high temperature combustion is modeled with a phenomenological approach which uses several fuel balance pools to represent different degrees of homogenization during partly homogeneous operating modes. A combined k-ε and density-difference approach is used to model the mixture formation during DI-modes. The developed model showed very good agreement with experimental results for homogeneous and partly homogeneous Diesel combustion with one set of parameters combined with very low computational time.

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The effects of fuel properties including ignitability, volatility, and compositions on operational range and combustion characteristics of premixed diesel combustion with various high volatility model fuels and an ordinary diesel fuel were examined in a DI diesel engine. The IMEP was limited by knocking with high intake oxygen concentrations and by unstable combustion or significant increases in CO and THC emissions with low intake oxygen concentrations regardless of fuels. The fuel volatility has little effect on the combustion characteristics and the stable operational range in premixed diesel combustion. With increasing octane number the combustion phasing is retarded and higher intake oxygen concentrations can be employed within the tolerance limits of rapid combustion, expanding the stable premixed diesel combustion IMEP range. The operational range of premixed diesel combustion with normal heptane and toluene blend fuels (NTF) shift to higher intake oxygen concentrations when compared with primary reference fuels (PRF) with the same research octane numbers, showing lower ignition characteristics than PRF. The silent, low NOx, and smokeless operation with high thermal efficiency was possible both with PRF and NTF when the intake oxygen concentration is optimized corresponding to IMEP.

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This paper presents numerical and experimental investigation of flame lift-off and stabilization mechanisms in heavy-duty diesel engines. The injection strategy, employing different nozzle configurations, allows quantification of the impact of varying inter-jet angle spacing in the presence of swirl. For this purpose, two different inter-jet angles are chosen in this study, 45° and 135°. Large-eddy simulations are performed, utilizing a detailed kinetic mechanism for n-heptane to resolve the turbulent fuel and air mixing and to capture the important species surrounding the ignition and flame-fronts to describe the flame stabilization process. Measurements are carried out for OH chemiluminescence to identify the flame lift-off position in an optical accessible engine. With decreasing inter-jet angle, it is shown that the impact of transportation of hot products from adjacent jets becomes more prominent. Hot reservoirs surrounding the lift-off length increase the local ambient temperature and augment the auto-ignition process by mixing of the cold injected fuel and hot air. When the inter-jet angle decreases, this effect becomes less important.

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Mixture formation and the chemical kinetics of combustion are examined in an automotive diesel engine operating at 1500 rpm and a fuel quantity corresponding to 3 bar gross IMEP. Laser-induced fluorescence of a toluene fuel tracer is used to obtain quantitative in-cylinder distributions of the fuel-air equivalence ratio, and homogeneous reactor simulations employing detailed chemistry are used to examine the impact of kinetics. With advanced combustion timing, losses in combustion efficiency and work output are found to be dominated by deficiencies in the mixture preparation process. With retarded injection, however, the chemical kinetics of combustion is the limiting factor. Trends in engine-out emissions are consistent with the measured mixture distributions and the results of the simulations.

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The spectral analysis of chemiluminescence of a PCCI diesel engine operating with moderately early injection timing was carried out in a single cylinder test engine. Investigations were conducted through direct visualization of the combustion phenomena with spectroscopic measurement of the intermediate species using a spectrometer coupled to ICCD camera. In order to understand the chemical kinetics of auto-ignition and combustion mechanism in PCCI engine, the spectral analysis of chemiluminescence was carried out. The following intermediate species were identified; OH^*, CH^*, CO-O recombination and formaldehyde (CH_2O) which marked the different combustion phases. Formaldehyde was detected in the low temperature oxidation (LTO) region and isolated clearly by high spectral resolution. The OH* radicals marked the regions with premixed fuel-air mixtures and high temperature oxidation (HTO) region. CH^* radicals were noted to mark well the fuel-rich region within the piston cavity after fuel impingement on the Derby hat wall. Soot formation arising from the fuel impingement on the Derby hat wall was oxidized in the late combustion phase. High temperature indicated by high intensity of OH^* radicals led to faster oxidation of the soot in the late combustion phase.

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Bio-fuels such as ethanol (EtOH) and ethyl tert-butyl ether (ETBE) are used as blending components in gasoline for carbon neutralization. These oxygenates are also recognized as high octane number fuels, which are acceptable for spark ignition (SI) combustion, as they inhibit end-gas auto-ignition (partly leading to knocking). However, for homogeneous charge compression ignition (HCCI) combustion, excess delay in ignition timing may occur as an undesirable effect, leading to misfiring or incomplete combustion. In this work, knocking phenomenon and HCCI combustion characteristics of ethanol and ETBE blended gasoline fuels with same octane numbers have been experimentally studied. Chemical reaction simulations were also conducted for further understanding. Experimental work was performed in a single cylinder gasoline engine with compression ratio set to 14.0. Intake air was heated at HCCI combustion operation. SI combustion test results show that when the same octane number fuels are used, ethanol and ETBE have no effect on knocking limit. On the other hand, HCCI combustion results indicate that ethanol retards ignition timing at low intake temperature condition, whereas ignition advancement is observed at high intake temperature condition. ETBE acted as an ignition accelerator for all intake temperatures. Based on these results, an empirical equation is proposed for HCCI timing prediction of the tested blended fuels.

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A novel injection strategy is proposed to realize PCCI combustion for marine diesels of large-bore and yet longer-stroke dimensions. This strategy utilizes a set of sprays from closely aligned holes having injection directions intersecting one another so as to cause mutual interaction and merger of the sprays by overlapping injection periods and applying different injection rates. It is feasible to improve the mixture stratification in a combustion chamber. Moreover, LCO (Light Cycle Oil) and its water-emulsification are newly introduced to realize the ignition control of PCCI combustion in this study. The potential of the strategy for PCCI combustion was successfully examined through observation of the spray merging process and combustion process in a rapid compression-expansion machine.

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Gasoline homogeneous charge induced ignition by diesel (HCII) uses port fuel injection of gasoline to form a homogeneous charge and direct injection of diesel fuel to ignite. Gasoline/diesel hybrid fuel (GDHF) mixes diesel and gasoline by a certain proportion and then is directly injected into the cylinder for combustion. So far some exploratory studies show that these two ways may merge the advantages of gasoline and diesel fuel to achieve high efficiency and low emission combustion targets. Combustion characteristics, emission characteristics, thermal efficiency and adaptability of low-temperature combustion have been comparatively investigated on a modified high-pressure common rail single-cylinder diesel engine. The results show that Both HCII and GDHF modes can achieve higher thermal efficiency than gasoline SI (spark ignition) combustion and achieve equal or even higher thermal efficiency than diesel CI (compression ignition) combustion. As gasoline ratio increases, the ignition delay of HCII mode remains almost the same, while the ignition delay of GDHF mode increases; the combustion duration in HCII and GDHF modes shortens significantly. With the increase of gasoline ratio, soot emissions reduce significantly and have a biggest reduction of 90%. Soot reduction of HCII is more significant compare to GDHF. Combined with EGR (Exhaust Gas Recirculation), both HCII and GDHF combustion modes can achieve low temperature combustion, with very low NOx and soot emissions.

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The Homogeneous Charge Compression Ignition (HCCI) is still a promising concept to optimize internal combustion (IC) engines with respect to emissions. The cycle-to-cycle variations of in-cylinder flow play an important role in HCCI combustion processes and can result in combustion instability due to the lean as well as knock combustion conditions. In order to characterize mentioned above effects, the Large Eddy Simulation (LES) has proved to be a reliable method. Multi-cycle LES based analysis has been carried out on a motored engine configuration to characterize the unsteady effects of HCCI combustion processes for both fully premixed mixture and early-direct spray injection cases. In-cylinder pressure and temperature as a function of crank angle were analyzed in terms of mean and standard deviation.

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The DI-PCCI combustion process with a high EGR ratio and early injection timing is simulated using a RANS-based commercial CFD code with an NMA combustion model. In addition, the formation processes of nitrogen oxide (NO), carbon monoxide (CO), and unburnt hydrocarbon (HC) are calculated. The calculation results are compared with the experimental data. According to the calculation results, the formation processes of NO, CO, and HC are discussed in relation to the spray development and ignition point. Furthermore, the combustion process of two-stage injection is also calculated. The result shows that the combustion process is described well by this model except in the case where auto-ignition occurs in the squish area. Additionally, the relationship between the combustion process and the mixture distribution is clarified. The main origins of the unburnt HC and CO emissions are located in the center region of the combustion chamber, where the mixture becomes excessively lean and low in temperature.

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Since the onset of Homogeneous Charge Compression Ignition (HCCI) combustion depends on the chemical reaction, it is quite difficult to control the start of combustion directly. Pulsed Flame Jet (PFJ), which is the jet of burning gas issuing from a small cavity facing a combustion chamber, has a potential for controlling the start of HCCI combustion in low-load conditions. In the present study, the characteristics of HCCI combustion initiated by PFJ were investigated using Rapid Compression Expansion Machine (RCEM). The validity of PFJ utilization was shown through pressure and NOx measurements.

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Width of engine bearings tends to be short because of the reductions in engine size and in power loss. Therefore short bearings, namely high surface pressure bearings, must be studied. In this study, friction of a con-rod bearing is evaluated with a mass conserving elastohydrodynamic lubrication model. Clearance shape, surface texture, and width of the bearing have been investigated. The friction of the bearing with a real clearance is less than that with a circle clearance. The surface textures having the character in circumferential direction have a tendency to lower the friction of the bearing. Property of oil is important especially on the short bearings.

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An accurate and robust equation for estimating instantaneous heat transfer coefficients has been developed. The equation has been derived from instantaneous surface temperature measurements on the combustion chamber wall of a direct-injection diesel engine. In a previous study, it was shown that the characteristics of the heat transfer coefficients inside and outside the cavity are different. In this study, the relationship between local combustion flame behavior and heat transfer coefficients has been investigated using 3D-CFD combustion simulation.

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Authors have previously examined the mechanism by which diesel soot emission is reduced when using Fischer-Tropsh Diesel (FTD) fuel compared with conventional diesel (JIS#2) fuel via Excitation-Emission Matrix analysis of polycyclic aromatic hydrocarbons (PAHs) and high-speed laser shadowgraphy of soot particles in the spray flame. As continuation, this study aims to compare properties of soot particles directly sampled in diesel spray flames fuelled with JIS#2 and FTD fuels by Transmission Electron Microscope (TEM). The diesel spray flame was achieved in a constant volume combustion chamber under diesel-like conditions (2.5MPa, 940K). Concentration, primary particle diameter, gyration radius and fractal dimension of soot aggregates were obtained from the TEM images of soot particles and compared between the two fuel cases.

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The reduction of fuel consumption and pollutant emission is the main objective in development of modern IC-engines. A promising method to achieve this is the use of DI-SI engines with a spray-guided mixture formation. One advantage in efficiency of direct injection is the evaporation cooling of the fuel, which allows a higher compression. Although the compression temperature inside the engine can be calculated easily from the boundary conditions, the resulting mixture is not homogeneous through the combustion chamber. Thus, a spatial and temporal resolved measurement of the temperature and fuel concentration during injection is required to locally resolve evaporation rate, mixing and cooling in the spray. An approved method to measure temperature and concentration with a high temporal and spatial resolution under engine relevant conditions is planar laser-induced fluorescence (PLIF). For measurements in the spray, 3-pentanone as fluorescence tracer is added to a non-fluorescent surrogate fuel. The spray of a multi-hole injector is excited quasi-simultaneously by two different excimer lasers (2-line LIF), the temperature and the vapor mass fraction of the fuel can then be calculated from the two signals. The measurements are conducted in a high temperature/pressure cell, where engine relevant conditions can be simulated. To quantify temperature and concentration correctly, a precise fluorescence calibration of the tracer in a flow cell as well as an optimized post processing strategy of the raw images is presented. The results of the measurement are compared to a CFD-simulation under same conditions.

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In this work, the RAYLIX measurement technique is applied for the first time in the combustion chamber of a direct injection, heavy duty Diesel engine. This technique is a combination of elastic Rayleigh scattering, laser induced incandescence, and extinction. When applied properly, it can provide spatially-resolved information about soot particle diameters, soot concentrations, and particle number densities in a measurement plane within the engine. Specially designed endoscopic optics are used in combination with an optically accessible heavy duty Diesel engine to evaluate the suitability of this measurement technique as a diagnostic tool in a close-to-production Diesel engine. A low-load operating point is chosen for the first application of the measurement technique. For both Diesel fuel and a Diesel-ethanol-water emulsion, results are presented for EGR rates of 0% and 30%. For the operating conditions presented here, it is demonstrated that EGR delays the onset of soot formation and decreases soot formation early in the combustion. The use of the Diesel-ethanol-water emulsion decreases early soot formation to an even greater extent.

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Surface temperature in internal combustion engines is of high interest when studying heat losses. Two approaches for retrieving the surface temperatures are thermocouples and Laser Induced Phosphorescence, LIP. This study aims to analyze LIP as a technique for measuring surface temperature in internal combustion engines. The motivation for this study is the need for accurate surface temperatures which can be used by predictive models and increase knowledge about heat transfer. In this work LIP measurements have been carried out in two optical engines. In the first engine a thermographic phosphor was applied on top of a metal piston. The second engine was fitted with a quartz liner which was coated with phosphor material. Several coating thicknesses have been tested and the LIP temperature was extracted from both opposing sides of the phosphor. Both engines were run in HCCI mode with reference fuels and electrically heated air. In a previous publication, the authors showed that a layer of phosphor can show different temperatures i.e. a higher temperature on the side facing the cylinder gas than on the side facing the wall. In this study it is shown which thickness is needed to accurately present the temperature for typical engine combustion. With an increasing thickness of the phosphor material, the surface gets gradually insulated and the phosphor temperature reading becomes inaccurate. LIP measurements from a quartz ring and a metal piston have been compared and the temperature increase during combustion is similar although the heat conductivity of quartz is 40-200 times smaller than the metal piston. Measurements with thermocouples often show a lower temperature increase than what is seen in the LIP results. The difference in heat conductivity between the phosphor coating and the underlying surface is of importance for understanding what temperature is actually measured.

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Exhaust gas temperature is an important factor in NO_x, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. Recently, as a measurement technique with high sensitivity and high response, laser diagnostics has been developed and applied to the actual engine combustions. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions. In this study, the theoretical and experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a computed tomography(CT) method using absorption spectra of water vapor at 1388nm. It has been demonstrated that the method has been successfully applied to engine exhausts to measure 2D temperature distributions.

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In-cylinder flow transition during a piston compression stroke was measured under motoring conditions using particle image velocimetry (PIV). A single-cylinder optical engine (bore diameter: 86 mm, stroke length: 86 mm, displacement volume: 500 cc) was used. This engine had quartz windows in the side of a pent roof, a quartz cylinder liner, and a quartz piston top. The two-dimensional velocity field along the center plane was measured. The temporal velocity change along the center plane and the size of the bulk flow were examined during the compression stroke. The turbulence intensity was calculated, and its distribution and temporal change were analyzed qualitatively. PIV measurements were conducted under four different engine speeds to investigate their effect on the in-cylinder turbulent flow field. The bulk flow velocity increased with the engine speed, but the flow pattern remained similar. The velocity of the bulk flow decreased and the turbulence intensity around the spark plug increased during the compression stroke. The turbulence intensity was a maximum around top dead center (TDC). These results describe the in-cylinder flow transition from large-scale bulk flow to small-scale turbulence.

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