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Recently the analysis of air-fuel mixing and combustion has become important under the stringent emissions regulations of diesel engines. In the case of gasoline engines, the KIVA computer program has been developed and used for the analysis of combustion. In this paper, the calculations of combustion phenomena in DI diesel engines are performed by modifying the KIVA program so as to be applicable to multi-hole nozzles and arbitrary patterns of injection rate. The thermophysical and ther-mochemical properties of gasoline are altered to those diesel fuel. In order to investigate the ability of this modified program, the calculations are compared with the experiments on single cylinder engines concerning the pressure, flame temperature and mass change of chemical species in cylinders. Furthermore, the calculation for the heavy duty DI diesel engine is performed with this diesel combustion program.

The concentrations of soot, NO and the other combustion products were measured by incylinder gas sampling in a DI diesel engine. The effects of injection timing, swirl ratio, and combustion chamber geometry on the formation and emission processes of soot and NO were studied. The following results were obtained: (1) Soot is promptly formed in the flame during the early combustion period where the equivalence ratio in the flame is high over 1.0. Thereafter almost all the formed soot is swiftly burnd up by oxidation during the middle combustion period. This process mainly determines the exhaust soot concentration. (2) NO is formed in the flame during the early and middle combustion period where the flame temperature is high over 2000 K. The highest NO concentration is observed at the flame tip swept by the air swirl. Though the concentration of the formed NO decreases by dilusion it nearly constant during the later combustion period.

The authors have developed a new partial flow dilution tunnel (hereafter referred to as PPFT), whose principal device is a flux splitting gas divider, as a new means of measuring particulate emissions which can be applied to transient cycle testing of diesel engines. The advantage of this system is that it can achieve perfect constant velocity splitting by means of its structure, and theoretically can also maintain high splitting performance despite fluctuations in the exhaust flow rate, including those due to engine exhaust pulsation. We compared this system with a full tunnel by analyzing the basic performance of the system and measuring particulate matter (PM) using an actual vehicle engine.

A variable valve timing (VVT) mechanism was applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead center are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, EGR, supercharging systems and high-pressure fuel injection equipment can simultaneously reduce NOx and smoke. The NOx and smoke suppression mechanism in the premixed diesel combustion was analyzed using the 3D-CFD code combined with detailed chemistry.

For reducing exhaust emissions of heavy-duty diesel engines, the authors made an experimental study of diesel combustion using a single cylinder engine. The engine performance and exhaust emissions have been measured using a wide range and high EGR rate under the conditions of high boost intake pressure. The engine test cell has been equipped the external supercharger that is able to raise the boost pressure to 500 kPa, and also equipped the EGR system to increase the EGR rate until 50% under the 500 kPa boost condition. In various test conditions of load and engine speeds the authors have obtained the results, that is, NOx has been reduced drastically without increasing Particulate Matter (PM).

The investigation of vehicle performances under on-road conditions has been required for emission reduction and energy saving in the real world. In this study, Real Car Simulation Bench (RC-S) was developed as an instrument for actual vehicle bench tests under on-road driving conditions, which could not be performed by using conventional chassis dynamometer (CH-DY). The experimental results obtained by RC-S were compared with the on-road driving data on the same car as used in RC-S tests. As a result, it was confirmed that RC-S could accurately reproduce the behavior of fuel consumption and exhaust emissions under on-road driving conditions.

Autoignition in the homogeneous charge compression ignition (HCCI) process typically exhibits heat release in two stages called cool flame and thermal flame. The mechanisms governing these two stages were investigated using a DME-fueled HCCI engine and numerical simulations. Composition analysis after cool flame showed that the cool flame is explained by a chain reaction mechanism in which the chain terminator is the intermediate species formed in cool flame. In the case of thermal flame, although the chain reaction mechanism is complex, the behavior is clearly described by thermal explosion theory in which the rate-determining reaction is H2O2 decomposition.

The 1997 Kyoto protocol came into effect in February, 2005 to reduce greenhouse gases within the period 2008-2012 by at least 5 % with respect to 1990 levels. Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because BDF is carbon neutral in principle. The purpose of this project is to produce a light-duty biodiesel truck which can be suitable for emission regulation in next generation. The effect of BDF on the performance and emissions of modern diesel engine which was equipped with the aftertreatment for PM and NOx emissions was investigated without modifications of engine components and parameters, as a first step for research and development of biodiesel engine. Rapeseed oil methyl ester (RME) was selected in behalf of BDF, and combustion characteristics, engine performance and exhaust emissions were made a comparison between RME and petroleum diesel fuel by steady operation and Japan transient mode (JE05) tests.

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

A soot model based on the kinetics of the formation of particles of carbon black, starting from radical nuclei to particle nuclei, is formulated and implemented to a 3 dimensional KIVA code. Model is capable of predicting total in-cylinder soot concentration and particle size distribution. Empirical parameters were tuned for the total soot emission of a single cylinder DI diesel engine. Model predicted results are quite consistent with reported experimental observations.

Reduction of exhaust emissions and BSFC has been studied using a high boost, a wide range and high-rate EGR in a Super Clean Diesel, six-cylinder heavy duty engine. In the previous single-turbocharging system, the turbocharger was selected to yield maximum torque and power. The selected turbocharger was designed for high boosting, with maximum pressure of about twice that of the current one, using a titanium compressor. However, an important issue arose in this system: avoidance of high boosting at low engine speed. A sequential and series turbo system was proposed to improve the torque at low engine speeds. This turbo system has two turbochargers of different sizes with variable geometry turbines. At low engine speed, the small turbocharger performs most of the work. At medium engine speed, the small turbocharger and large turbocharger mainly work in series.

In heavy duty diesel engines, waste heat recovery systems are remarkable means for fuel consumption improvement. In this paper, Diesel-Rankine combined cycle which is combined diesel cycle with Rankine cycle is studied to clarify the quantitative potential of fuel consumption improvement with a high EGR rate and high boosted diesel engine. The high EGR rate and high boosted diesel engine of a single cylinder research engine was used and it reaches brake specific fuel consumption (BSFC) of 193.3 g/kWh at full load (BMEP=2.0MPa). And its exhaust temperature reaches 370 C. The exhaust gas temperature does not exceed 400 C in high boosted diesel engine even at full load operating condition because of a high excess air ratio. On the other hand, exhaust gas quantity is larger due to a high boosting.

A natural gas direct injection test engine equipped with a newly developed natural gas injector was built. High total hydrocarbon (THC) emission at part-load and high NOx emission at high-load remain as problems for direct injection natural gas engines. THC reduction and combustion improvement by throttling and NOx reduction by EGR were investigated. The following results were obtained: (1) the combustion at light and medium load conditions is improved by throttling. It is possible to improve the thermal efficiency at light-load in spite of the pumping loss by throttling. THC emissions are greatly decreased in this condition; (2) a large NOx reduction can be obtained without combustion deterioration by appropriate EGR at high-load conditions; and (3) it is possible to decrease both THC and NOx emissions by both throttling and EGR at part-load conditions.

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (LII) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the LII and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both LII and SMPS.

Simulations of DI Diesel engine combustion have been performed using a modified KIVA-II package with a recently developed phenomenological soot model. The phenomenological soot model includes generic description of fuel pyrolysis, soot particle inception, coagulation, and surface growth and oxidation. The computational results are compared with experimental data from a Cummins N14 single cylinder test engine. Results of the simulations show acceptable agreement with experimental data in terms of cylinder pressure, rate of heat release, and engine-out NOx and soot emissions for a range of fuel injection timings considered. The numerical results are also post-processed to obtain time-resolved soot radiation intensity and compared with the experimental data analyzed using two-color optical pyrometry. The temperature magnitude and KL trends show favorable agreement.

Degradation of the deNOx performance has been found in in-use heavy-duty vehicles with a urea-SCR system in Japan. The causes of the degradation were studied, and two major reasons are suggested here: HC poisoning and deactivation of pre-oxidation catalysts. Hydrocarbons that accumulated on the catalysts inhibited the catalysis. Although they were easily removed by a simple heat treatment, the treatment could only partially recover the original catalytic performance for the deNOx reaction. The unrecovered catalytic activity was found to result from the decrease in conversion of NO to NO2 on the pre-oxidation catalyst. The pre-oxidation catalyst was thus studied in detail by various techniques to reveal the causes of the degradation: Exhaust emission tests for in-use vehicles, effect of heat treatment on the urea-SCR systems, structural changes and chemical changes in active components during the deactivation were systematically investigated.

Key requirements of engines for vehicles are large output power and high efficiency, low emission as well as small size and light weight. Hydrogen combustion engines with direct injection have the characteristics to meet these factors. Tokyo City University, former Musashi Institute of Technology, has studied hydrogen fueled engines with direct injection since 1971. The key technology in the development of hydrogen fueled engines is the hydrogen injector for direct injection with the features such as high injection rate, high response and no hydrogen gas leakage from the needle valve of the hydrogen injector. A common-rail type system to actuate the needle valves of the high pressure hydrogen injectors was intentionally applied to fulfill good performances such as large injection rate, high response and no hydrogen gas leakage.

Recently, after-treatment techniques for diesel engine emission have made remarkable progress with the development of suitable De-NOx catalysts. The urea-injection SCR system is one of the candidates for a high efficiency De-NOx method for diesel engine emissions. This system reduces NOx through a reaction with ammonia (NH3) that is generated from injected urea. In this system, it is very important to control the amount and timing of the urea injection so as to minimize the NH3 gas slip. Therefore, NH3 gas measurement is becoming important during the development of NOx after-treatment systems even though NH3 is not a target component of the current emission regulations. In this paper, a new NH3 gas analyzer utilizing a chemi-luminescence detection (CLD) method has been developed. The new NH3 analyzer consists of dual detectors (DCLDs) and a furnace for a NH3 oxidization catalyst. Real-time concentration of NH3 can be calculated from the difference of NOx readings of two detectors.

The biomass fuel is expected to solve the global warming due to a carbon neutral. A rapeseed oil methyl ester (RME) as biomass fuel was selected, and also a low sulfur diesel fuel is tested as reference fuel in this study. The experiments were carried out to improve diesel emissions and engine performance using high boost and high rate EGR system and a common rail injection system in a single cylinder engine. The diesel emissions and engine performance have been measured under the experimental conditions such as charging boost pressure from atmospheric pressure to 401.3kPa maximum and changing EGR rate from 0% to 40% maximum. RME contain about 10 mass % oxygen in the fuel molecule. Furthermore, RME does not contain aromatic hydrocarbons in the fuel. Due to these chemical properties, RME can be used at 40% high EGR condition.

The bore scope system can visualize not only diesel combustion in the research engine but also in actual diesel combustion in a multi-cylinder engine. The experimental engine has 2.0-liter displacement and has an external supercharger with up to two times the boost pressure of the naturally aspirated engine condition. The video camera used for this study is nac GX-1. From observed data under the several experimental conditions such as increased injection pressures, swirl ratios, and EGR rates, the flame temperature and KL factor were obtained by two-color method analysis. The diesel combustion processes are understood well by analyzing high-speed movies of the diesel flame motion and its temperature. NOx and smoke are mutually related to maximum flame temperature even in an engine with low NOx emission and lean smoke. It is reconfirmed as necessary to maintain a maximum flame temperature of 2,000–2,200K to reduce emissions of NOx and smoke simultaneously.