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NOx emissions from diesel passenger vehicles affect the atmospheric environment. It is difficult to evaluate the NOx emissions influenced by environmental conditions such as humidity and temperature, traffic conditions, driving patterns, etc. In the authors’ previous study, real-driving experiments were performed on city and highway routes using a diesel passenger car with only an exhaust gas recirculation system. A statistical prediction model of NOx emissions was considered for simple estimations in the real world using instantaneous vehicle data measured by the portable emissions measurement system and global positioning system. The prediction model consisted of explanatory variables, such as velocity, acceleration, road gradient, and position of transmission gear. Using the explanatory variables, NOx emissions on the city and highway routes was well predicted using a diesel vehicle without NOx reduction devices.

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.

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.

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.

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).

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 engine in the research is a single cylinder DI diesel using the emission reduction techniques such as high boost, high injection pressure and broad range and high quantity of exhaust gas recirculation (EGR). The study especially focuses on the reduction of particulate matter (PM) under the engine operating conditions. In the experiment the authors measured engine performance, exhaust gases and mass of PM by low sulfur fuel such as 3 ppm and low sulfur lubricant oil such as 0.26%. Then the PM components were divided into soluble organic fraction (SOF) and insoluble organic fraction (ISOF) and they were measured at each engine condition. The mass of SOF was measured from the fuel fraction and lubricant oil fraction by gas chromatography. Also each mass of soot fraction and sulfate fraction was measured as components of ISOF. The experiment was conducted at BMEP = 2.0 MPa as full load condition of the engine and changing EGR rate from 0% to 40 %.

Urea SCR (Selective Catalytic Reduction) system has high potential of reducing NOx. But such as system durability and safety under deteriorated catalysts conditions have not been well enough clarified because it is new technology for vehicles. In this paper, current NOx emission level of an engine equipped with urea SCR system is discussed and then exhaust emission characteristics were analyzed when the SCR catalyst and/or oxidation catalyst lose their functions. When both SCR and oxidation catalyst were de-activated, not only NOx but also PM increased remarkably, which were much more than the engine-out emissions. Oxidation catalyst downstream of SCR catalyst was effective to suppress such deteriorations.

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.

In the previous study design of two-component normal paraffin fuel was attempted considering the components and blending ratio. Only the thermodynamic analysis of combustion and analysis of emission characteristics were performed to evaluate the design performance. In this study mixture formation behavior and combustion phenomena of pure and mixed n-paraffin fuels were investigated by direct visualization in an AVL engine with bottom view piston. The experiments included laser-illuminated high-speed photography of the fuel injection phase and combustion phase to investigate physical differences. The results obtained for the proposed fuels are compared with the results of conventional diesel fuel. It was found that the two component normal paraffin fuels with similar thermo physical properties have very similar spray development pattern but evaporation rates are different.

Fuel formulation for premixed charge compression ignition (PCCI) combustion has been attempted based on the mixture formation and auto-ignition behavior of normal paraffin fuels. Different pure and mixed fuels with different blending ratios are tested. The mixture formation behavior is investigated photographically in a constant volume combustion chamber (CVCC) at elevated temperature and pressure. Auto-ignition behavior is tested in a Fuel Ignition Analyzer under different test conditions. It is found that the evaporation rate of pure n-paraffin fuel increases and the ignition delay becomes longer with decreases in the chain length. In the range of test condition used in this study, the flash-boiling phenomenon affects the fuel evaporation rate and ignition delay to some extent. Based on the experimental results a mixture of a very light mixture promoting component (MPC) and a moderately dense igniting component (IC) at a ratio of 3:1 is found to be optimum for PCCI combustion.

To clarify the effect of fuel properties on diesel exhaust emissions, direct injection of two component fuels with approximately zero aromatic content and sulfur were attempted in a diesel engine. Fuels were prepared using paraffins having different cetane numbers and boiling points. Parameters considered are the Average Boiling Point (ABP) by volume and the difference of component characteristics for the same ABP. The results indicate that the trade off relation between NOx and particulate matter (PM) emissions depends significantly on ABP or density and is independent of the fuel component. On the other hand, components of the mixed fuels have significant influence on SOF and THC emissions. Fuels having higher amount of low boiling point components emit higher THC. Mixtures of low boiling point-high cetane number fuel and high boiling point-low cetane number fuel or fuel that contains normal paraffins only emit higher SOF.

Nitrous oxide (N2O) is a strong green house effect gas and three-way catalyst is one of the major sources. N2O is mostly emitted at temperatures during the process of light off in the catalyst and the frequency of this temperature range over total temperature range distribution affects strongly on N2O emission. The effect of cold ambient on N2O emission was analyzed based on N2O-catalyst temperature characteristics and catalyst temperature data gained by road driving test at north part of Japan in winter. As results, N2O emission may drastically increase in colder cities and winter city traffic conditions.

To derive an effective technique for reducing a greenhouse gas nitrous oxide (N2O) emitted from automobiles, we prepared experimental three-way catalysts carrying various types and quantities of precious metals, and investigated their N2O generation and conversion characteristics. In view of previous reports on increased N2O emissions from in-use automobiles, we deactivated the catalysts in a rapid aging test, and observed the effect of catalyst deactivation on N2O generation and conversion by the catalysts. We found that the concentrations of generated N2O decreased as the quantities of precious metals carried by catalysts were decreased and that, accordingly, these low-carrying catalysts are more advantageous from the standpoint of reducing N2O generation. However, the concentrations of generated N2O increased as the catalysts were deactivated.

Under heavy load condition, single fuel operation with diesel fuel was studied experimentally for the homogeneous charge diesel combustion (HCDC) method. HCDC engine, in which pre-mixture was formed by fuel injected into an intake manifold and mixed with air beforehand then ignited by small amount of fuel directly injected into a cylinder, can reduce NOx and smoke simultaneously from the diesel engine. In HCDC the higher the premixed fuel ratio was, the lower the emissions were. Accordingly, it was indicated that homogeneous pre-mixture contributed to improvement of exhaust emissions. However, a diesel knocking due to uncontrolled self-ignition may occur under high premixed fuel ratio conditions in the case of operating heavy loads. Thus, the maximum amount of premixed fuel was restricted by these knocking limits.

To find a clue to reduction techniques for Nitrous Oxide (N2O) emission from three-way catalyst equipped vehicles, four test samples of three-way catalysts with typical noble metal compositions were fabricated by way of experiment and their N2O formation characteristics have been experimentally studied. Then, these catalyst samples were conditioned artificially by aging with real automotive exhaust gas and the N2O formation characteristics after aging has been also observed. As results, catalyst temperature zones and concentration levels of N2O formation varies greatly by the catalyst composition. In general, a catalyst with lower metal content showed lower N2O mass emission at both fresh and after aging conditions. The tendency of the increase in N2O mass emission due to the deterioration is also different among the tested catalyst samples.

A homogeneous Charge Compression Ignition Diesel Combustion (HCDC) system has been experimentally studied for it's effect on exhaust purification of diesel engines. In this system, most fuel is injected into the intake manifold to form homogeneous pre-mixture in the combustion chamber beforehand and the pre-mixture is ignited with a small amount of fuel directly injected into the cylinder by a conventional injection system. Because this system performs homogeneous lean-burn, it can realize low emission which cannot be realized by conventional diesel engines without impairing ignition controllability in the operations ranging from idle to full load. In particular, although the operating regions were strictly limited, extremely low Nox emission levels of as low as 10 to 40 ppm were realized with maintaining low smoke emissions, when the ratio of pre-mixed fuel was increased up to approx. 98%.

An experimental and a numerical analysis wereconducted based on the concept of homogeneous charge diesel combustion (HCDC), in which most of the fuel is supplied for pre-mixed homogeneous charge which is compressed in the cylinder and then ignited by small amount of diesel fuel directly injected into a cylinder. At the previous report, It was indicated that simultaneous improvement of NOx and smoke were possible. Especially under a certain condition, NOx was extremely reduced. This report describes the preliminary analysis for the cause of this emission improvement with HCDC method. As result, direct optical observation of the combustion phenomena and numerical analysis using KIVA2 code suggested that low NOx combustion may be caused by lowered combustion temperature and reduced combustion period due to the uniform lean combustion.