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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).

This study analyzes the factors influencing the thermal efficiency of a homogeneous charge spark-injection (SI) engine fuelled with hydrogen, focusing on the degree of constant volume and cooling loss. The cooling loss from the burning gas to the cylinder walls is quantitatively evaluated by analyzing the cylinder pressure diagram and exhaust gas composition. The degree of constant volume burning and constant volume cooling are also obtained by fitting the Wiebe function to the rate of heat release calculated using the cylinder pressure diagram. A comparison of combustion and cooling characteristics of hydrogen and methane combustion reveals that cooling loss in hydrogen combustion is higher than that of methane combustion due to the short quenching distance and rapid burning velocity during hydrogen combustion. It is also suggested that the high cooling loss observed during hydrogen combustion reduces thermal efficiency.

Characteristics of methane direct injection spark ignition stratified combustion in lean hydrogen mixture were analyzed both in a single cylinder engine and in a constant volume combustion vessel. Combustion pressure and instantaneous combustion chamber wall temperature during combustion process were measured and used in analysis of combustion and cooling loss. Results in this research show the premixed hydrogen increases cooling loss to combustion chamber wall while achieving combustion promotion, and the combustion system is effective especially in lean mixture conditions. Analysis of flame propagation was also done with schlieren photography in the constant volume combustion vessel.

The effects of intake dilution with various dilution gases including nitrogen, argon, and carbon dioxide on low temperature diesel combustion were investigated in a naturally aspirated DI diesel engine to understand the mechanism of the simultaneous reductions in smoke and NOx with ultra-high EGR. NOx almost completely disappears with the intake oxygen concentration diluted below 16% regardless of the kind of dilution gas. Smoke emissions decrease with increased heat capacity of the charged gas due to promotion of mixture homogeneity with longer ignition delays. Intake dilution with the 36% CO2 + 64% Ar mixture which has a similar specific heat capacity as N2 shows lower smoke emissions than with N2. Chemical kinetics analysis shows that carbon dioxide may help to reduce NOx and soot by lowering the reaction temperature as well as by changing the concentrations of some radicals or/and species related to soot and NOx formation.

Reformed fuel from hydrocarbons or alcohol mainly consists of hydrogen, carbon monoxide and carbon dioxide. The composition of the reformed fuel can be varied to some extent with a combination of a thermal decomposition reaction and a water gas shift reaction. Methanol is known to decompose at a relatively low temperature. An application of the methanol reforming system to an internal combustion engine enables an exhaust heat recovery to increase the heating value of the reformed fuel. This research analyzed characteristics of combustion, exhaust emissions and cooling loss in an internal combustion engine fueled with several composition of model gases for methanol reformed fuels which consist of hydrogen, carbon monoxide and carbon dioxide. Experiments were made with both a bottom view type optical access single cylinder research engine and a constant volume combustion chamber.

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.

A new concept DISC engine equipped with a two-stage injection system was developed. The engine was modified from a single cylinder DI diesel engine with large cylinder diameter (135mm). Combustion characteristics and exhaust emissions with regular gasoline were examined, and the experiments were also made with gasoline-diesel fuel blends with higher boiling temperatures and lower octane numbers. To realize stratified mixture distribution in combustion chamber flexibly, the fuel was injected in two-stages: the first stage was before the compression stroke to create a uniform premixed lean mixture and the second stage was at the end of the compression stroke to maintain stable ignition and faster combustion. In this paper, the effect of the two-stage injection on combustion and exhaust emissions were analyzed under several operating conditions.

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.

The dependence of ultra-high EGR low temperature diesel combustion on fuel properties including cetane number and distillation temperature was investigated with a single-cylinder, naturally aspirated, 1.0 L, common rail DI diesel engine. Decreasing cetane number in fuels significantly reduces smoke emission due to an extension in ignition delay and the subsequent improvement in mixture formation. Smokeless combustion, ultra-low NOx, and efficient operating range with regard to EGR and IMEP are significantly extended by decreasing fuel cetane number. Changes in fuel distillation temperature do not result in significant differences in smoke emission and thermal efficiency for ultra-high EGR operation, and smokeless operation is established even with higher distillation temperature fuels as long as fuel cetane number is sufficiently low.

The new 2GR-FKS / FXS engines were developed to achieve stringent fuel economy and emission targets and respond to recent innovations in the field. The major parts of the 2GR-FKS/FXS engines were re-designed based on the well-received dynamic performance and fuel economy aspects of the 2GR-FE engine. The aims of this development were as follows. 1 Best-in-class power performance 2 Environmental performance that maximizes thermal efficiency and complies with fuel economy and emission regulations in each country by a wide margin 3 Engine response typical of V6 engines through drastic weight reduction of moving parts To achieve these conflicting aims, the developed engines use a modified version of the D-4S fuel injection system, which enables selective use of direct and port injection, in addition to advanced technologies such as variable valve technology (VVT) with a mid-position lock system and an exhaust port cooling system.

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 use of biodiesel fuels as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO2 emission, because biodiesel is produced from renewable biomass resources. Biodiesel is usually blended to conventional diesel fuel in various proportions. It is possible that this biodiesel blending causes the problems on emission characteristics of modern diesel engine, because it could be confirmed that the application of neat biodiesel to modern diesel engines whose control parameters were optimized for conventional diesel fuel deteriorated the emission performances. It is necessary to clarify the effect of biodiesel blending on exhaust emissions of modern diesel engine. Rapeseed oil methyl ester (RME) was selected as a biodiesel used in this study.

The use of biomass fuels for vehicles has been a focus of attention all over the world in terms of prevention of global warming, effective utilization of resources and local revitalization. For the purpose of beneficial use of unused biomass resources, the movement of the use of bioethanol and biodiesel made from them has spread in Japan. In Japan, biodiesel is mainly made from waste cooking oil collected by local communities or governments, and in terms of local production for local consumption, it is used as neat fuel (100% biofuel) or mixed with diesel fuel in high concentration for the vehicles. On the other hand, extremely low emission level must be kept for not only gasoline vehicles but also diesel vehicles in the post new long-term regulation implemented from 2009 in Japan.

The effect of boiling point difference as well as the flash boiling of two-component normal paraffin fuels on combustion and exhaust emission has been examined under different test conditions. To obtain a wide variation in boiling point between components different high boiling point fuels (n-undecane, n-tridecane and n-hexadecane) were blended with a low boiling point fuel (n-pentane) and different low boiling point fuels (n-pentane, n-hexane, and n-heptane) were blended with a high boiling point fuel (n-hexadecane). In addition the volume fraction of n-pentane was varied to have the best mixture ratio with n-tridecane. These fuel combinations exhibit different potential for flash boiling based on a certain ambient condition. The results indicate that though the potential for flash boiling is the highest for a mixture of n-pentane and n-hexadecane it emits about 20% higher PM than a mixture of n-pentane and n-tridecane.

Unregulated emissions from a DI diesel engine with ultra-high EGR low temperature combustion were analyzed using Fourier transform infrared (FTIR) spectroscopy and the reduction characteristics of both regulated and unregulated emissions by two exhaust catalysts were investigated. With ultra-high EGR suppressing the in-cylinder soot and Nox formation as well as with the exhaust catalysts removing the engine-out THC and CO emissions, clean diesel operation in terms of ultra-low regulated emissions (Nox, PM, THC, and CO) is established in an operating range up to 50% load. To realize smokeless low temperature combustion at higher loads, EGR has to be increased to a rate with the overall (average) excess air ratio less than the stoichiometric ratio.

Reduction of exhaust emissions and BSFC was studied for high pressure, wide range, and high EGR rates in a Super-clean Diesel six-cylinder heavy duty engine. The GVW 25-ton vehicle has 10.52 L engine displacement, with maximum power of 300 kW and maximum torque of 1842 Nm. The engine is equipped with high-pressure fuel injection of a 200 MPa level common-rail system. A variable geometry turbocharger (VGT) was newly designed. The maximum pressure ratio of the compressor is about twice that of the previous design: 2.5. Additionally, wide range and a high EGR rate are achieved by high pressure-loop EGR (HP-EGR) and low pressure-loop EGR (LP-EGR) with described VGT and high-pressure fuel injection. The HP-EGR can reduce NOx concentrations in the exhaust pipe, but the high EGR rate worsens smoke. The HP-EGR system layout has an important shortcoming: it has great differences of the intake EGR gas amount into each cylinder, worsens smoke.

The emission reduction from diesel engines is one of major issues in heavy duty diesel engines. Super Clean Diesel (SCD) Engine for heavy-duty trucks has also been researched and developed since 2002. The main specifications of the SCD Engine are six cylinders in-line and 10.5 l with a turbo-intercooled and cooled EGR system. The common rail system, of which the maximum injection pressure is 200 MPa, is adopted. The turbocharger is capable of increasing boost pressure up to 501.3 kPa. The EGR system consists of both a high-pressure loop (HP) EGR system and a low-pressure loop (LP) EGR system. The combination of these EGR systems reduces NOx and PM emissions effectively in both steady-state and transient conditions. The emissions of the SCD Engine reach NOx=0.2 g/kWh and PM=0.01 g/kWh with aftertreatment system. The adopted aftertreatment system includes a Lean NOx Trap (LNT) and Diesel Particulate Filter (DPF).

Lean NOx trap (LNT) and Urea-SCR system are effective aftertreatment systems as NOx reduction device in diesel engines. On the other hand, DPF has already been developed as PM reduction device and it has been used in various vehicles. LNT can absorb and reduce NOx emission in wide range exhaust temperatures, from 150°C to 400°C, and the size of LNT component can be compact in comparison with Urea-SCR system because LNT uses the diesel fuel as a reducing agent and it is needless to install the reducing agent tank in the vehicle. In this study, authors have shown that the NOx conversion rate of LNT is high in the case of extremely low NOx concentration from the engine. Also, the effects of LNT and DPF were examined using the Super Clean Diesel (SCD) Engine, which has low NOx level before aftertreatment and has been finished as Japanese national project.