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Urea SCR (Selective Catalytic Reduction) exhaust after-treatment systems are one of the most promising measures to reduce NOx emissions from diesel engines. Both Cu-zeolite (Cu-SCR) and Fe-zeolite (Fe-SCR) urea SCR systems have been studied extensively but not many detailed studies have been conducted on the combination of both systems. Thus, we carried out studies on such Combined-SCR systems and their capability to reduce NOx under various engine operating conditions. We also conducted transient engine tests using different catalyst systems to compare their performance. The results show that combined-SCR systems can reduce NOx more effectively than Fe-SCR or Cu-SCR alone. The best NOx reduction performance was achieved at a Cu ratio of 0.667 (i.e. Fe: Cu =1: 2). Combined-SCR thus apparently benefits from the characteristics of both Cu-SCR and Fe-SCR, allowing it to reduce NOx over a wide range of operating conditions.

Widespread use of biofuels for automobiles would greatly reduce CO2 emissions and increase resource recycling, contributing to global environmental conservation. In fact, activities for expanding the production and utilization of biofuels are already proceeding throughout the world. For diesel vehicles, generally, fatty acid methyl ester (FAME) made from vegetable oils is used as a biodiesel. In recent years, hydrotreated vegetable oil (HVO) has also become increasingly popular. In addition, biomass to liquid (BTL) fuel, which can be made from any kinds of biomass by gasification and Fischer-Tropsch process, is expected to be commercialized in the future. On the other hand, emission regulations in each country have been tightened year by year. In accordance with this, diesel engines have complied with the regulations with advanced technologies such as common-rail fuel injection system, high pressure turbocharger, EGR and aftertreatment system.

The use of biofuel is essential for the reduction of greenhouse gas emission. This study highlights the use of biodiesel as a means of reducing greenhouse gas emission from the diesel engine of heavy-duty vehicles. Biodiesel is fatty acid methyl ester (FAME) obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. The CO2 emission from combustion of biodiesel is defined to be equivalent to the CO2 volume absorbed by its raw materials or plants in their course of growth. On the other hand, however, operation of diesel engine with biodiesel is known to increase the NOx emission when compared with that with conventional diesel fuel. Then suppressing this NOx increase is regarded as a critical issue. This paper consists of two parts: comprehending the factors of NOx emission increase and improving this emission performance in a diesel engine fuelled with biodiesel.

As a technology required for future commercial heavy-duty diesel engines, this study reexamines the potential of the multiple injection strategy for improving the thermal efficiency while maintaining low engine-out exhaust emissions with a high EGR rate of more than 50% and high boost pressure of 276.3 kPa abs under medium load conditions. The experiments were conducted with a single cylinder research engine. The engine was operated at BMEP of 0.8 MPa at a medium speed. Using multiple injections, the temporal and spatial in-cylinder temperature distribution was changed to investigate the effect on fuel consumption and exhaust emissions. The results showed that the multiple injection strategy combined with higher EGR rate could improve fuel consumption by about 3% due to the reduction of heat loss from the wall.

N₂O is known to have a significantly high global warming potential. We measured N₂O emissions in engine-bench tests by changing the NO/NH₃ ratio and exhaust gas temperature at the oxidation catalyst inlet in a heavy-duty diesel engine equipped with a urea SCR (selective catalytic reduction) system. The results showed that the peak N₂O production ratio occurred at an exhaust gas temperature of around 200°C and the maximum value was 84%. Moreover, the N₂O production ratio increased with increasing NO/NH₃. Thus, we concluded that N₂O is produced via the NO branching reaction. Based on our results, two methods were proposed to decrease N₂O formation. At low temperatures ~200°C, NO should be reduced by controlling diesel combustion to lower the contribution of NO to N₂O production. This is essential because the SCR system cannot reduce NOx at low temperatures.

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.

The use of biofuel is essential for the reduction of greenhouse gas emission. This paper highlights the use of biodiesel as a means of reducing greenhouse gas emission from the diesel engine of heavy-duty vehicles. Biodiesel is fatty acid methyl ester (FAME) obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. The CO₂ emission from combustion of biodiesel is defined to be equivalent to the CO₂ volume absorbed by its raw materials or plants in their course of growth. On the other hand, however, biodiesel is known to increase the NOx emission when compared with operating with conventional diesel fuel, then suppressing this increase is regarded as a critical issue. This study is intended to identify the fuel properties of biodiesel free from increase in the NOx emission.

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 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 application of biodiesel 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. In Japan, neat biodiesel derived from waste cooking oil has often been applied to commercial vehicles. However, it is possible that the difference of fuel properties between conventional diesel fuel and biodiesel causes the problems on exhaust emission characteristics of diesel engine. Therefore, it is necessary to clarify the effect of biodiesel fuelling on exhaust emissions from commercial vehicles. Light-duty garbage trucks and heavy-duty diesel buses which were actually fueled with biodiesel in Kyoto, Japan, were used for test vehicles in this study. The exhaust emissions from these vehicles during JE05 mode tests were compared between biodiesel derived from waste cooking oil and conventional diesel fuel.

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.

For reducing NOx emissions, EGR is effective, but an excessive EGR rate causes the deterioration of smoke emission. Here, we have defined the EGR rate before the smoke emission deterioration while the EGR rate is increasing as the limiting EGR rate. In this study, the high rate of EGR is demonstrated to reduce BSNOx. The adapted methods are a high fuel injection pressure such as 200 MPa, a high boost pressure as 451.3 kPa at 2 MPa BMEP, and the air intake port that maintains a high air flow rate so as to achieve low exhaust emissions. Furthermore, for withstanding 2 MPa BMEP of engine load and high boosting, a ductile cast iron (FCD) piston was used. As the final effect, the installations of the new air intake port increased the limiting EGR rate by 5%, and fuel injection pressure of 200 MPa raised the limiting EGR rate by an additional 5%. By the demonstration of increasing boost pressure to 450 kPa from 400 kPa, the limiting EGR rate was achieved to 50%.

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).

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.

A urea SCR system was combined with a DPF system to reduce NOx and PM in a four liters turbocharged with intercooler diesel engine. Significant reduction in NOx was observed at low exhaust gas temperatures by increasing NH3 adsorption quantity in the SCR catalyst. Control logic of the NH3 adsorption quantity for transient operation was developed based on the NH3 adsorption characteristics on the SCR catalyst. It has been shown that NOx can be reduced by 75% at the average SCR inlet gas temperature of 158 deg.C by adopting the NH3 adsorption quantity control in the JE05 Mode.

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 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.

In order to discuss future technical issues for urea SCR (selective catalytic reduction) system, it is necessary to assess various technical possibilities that would be applied to urea SCR systems which is capable of complying with future emission level requirements, for example Japanese 2009 emission regulation. In this paper, three measures (enhanced insulation on a DOC (diesel oxidation catalyst), aggressive urea solution injection and idling stop) are installed on a urea SCR system of a commercial engine system in order to achieve further NOx (nitrogen oxide) reductions. With combination of these three measures, NOx is drastically reduced to the levels lower than 0.7 g/kWh, which is a NOx limit value of the Japanese 2009 emission regulation. NH3 (ammonia) and HCN (hydro cyanide) are also measured as unregulated harmful components.

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because bio-diesel is carbon neutral in principle. However, when biodiesel was applied to conventional diesel engines without modification for biodiesel, NOx emission was increased by the change in fuel characteristics. It is necessary to introduce some strategies into diesel engines fuelled with biodiesel for lower NOx emission than conventional diesel fuel case. The purpose of this study is to reveal that exhaust gas recirculation (EGR) is one of the solutions for the reduction of NOx emission and meeting the future emission regulations when using biodiesel. Neat Rapeseed oil methyl ester (RME) as a biodiesel (B100) was applied to diesel engines equipped with high pressure loop (HPL) EGR system and low pressure loop (LPL) EGR system. Cooled HPL EGR was increased during steady-state operations and JE05 transient mode tests.

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because biodiesel is carbon neutral in principle. However, biodiesels yield an increase in NOx emission from conventional diesel engine, compared with diesel fuel case. Therefore, some strategies are needed for meeting the future emission regulations when using biodiesel. In this study, rapeseed oil methyl ester (RME) was applied to diesel engine equipped with exhaust gas recirculation (EGR) system and NOx storage reduction (NSR) catalyst. NOx reduction rate of NSR catalyst was drastically decreased by using RME, even if injection quantity of RME for rich spike was enhanced. However, an increase in EGR rate could reduce NOx emission without the deterioration in smoke and PM emissions.