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Nissan’s variable compression turbo (VC-Turbo) engine has a multilink mechanism that continuously adjusts the top and bottom dead centers of the piston to change the compression ratio and achieve both fuel economy and high power performance. Increasing the exhaust gas recirculation (EGR) rate is an effective way to further reduce the fuel consumption, although this increases the exhaust gas condensation in the cylinder bores, causing a more corrosive environment. When the EGR rate is increased in a VC-Turbo engine, the combined effect of piston sliding and exhaust gas condensation at the top dead center accelerates the corrosive wear of the thermal spray coating. Stainless steel coating is used to improve the corrosion resistance, but the adhesion strength between the coating and the cylinder bores is reduced.

Dilution combustion with exhaust gas recirculation (EGR) has been applied for the improvement of thermal efficiency. In order to stabilize the high diluted combustion, it is important to form an appropriate turbulence in the combustion cylinder. Turbulent intensity needs to be strengthened to increase the combustion speed, while too strong turbulence causes ignition instability. In this study, the factor of combustion instability under high diluted conditions was analyzed by using single cylinder engine test, optical engine test and 3D CFD simulation. Finally, methodology of in-cylinder flow design is attempted to build without any function by taking into account the representative scales of turbulence and premixed combustion.

Technologies for improving the fuel economy of gasoline engines have been vigorously developed in recent years for the purpose of reducing CO2 emissions. Increasing the compression ratio is an example of a technology for improving the thermal efficiency of gasoline engines. A significant issue of a high compression ratio engine for improving fuel economy and low-end torque is prevention of knocking under a low engine speed. Knocking is caused by autoignition of the air-fuel mixture in the cylinder and seems to be largely affected by heat transfer from the intake port and combustion chamber walls. In this study, the influence of heat transfer from the walls of each part was analyzed by the following three approaches using computational fluid dynamics (CFD) and experiments conducted with a multi-cooling engine system. First, the temperature rise of the air-fuel mixture by heat transfer from each part was analyzed.

On-board hydrogen generation technology using a fuel reforming catalyst is an effective way to improve the fuel efficiency of automotive internal combustion engines. The main issue to be addressed in developing such a catalyst is to suppress catalyst deterioration caused by carbon deposition on the catalyst surface due to sulfur adsorption. Enhancing the hydrocarbon and water activation capabilities of the catalyst is important in improving catalyst durability. It was found that the use of a rare earth element is effective in improving the water activation capability of the catalyst. Controlling the hydrocarbon activation capability of the catalyst for a good balance with water activation was also found to be effective in improving catalyst durability.

To improve the fuel economy via high EGR, combustion stability is enhanced through the addition of hydrogen, with its high flame-speed in air-fuel mixture. So, in order to realize on-board hydrogen production we developed a fuel reformer which produces hydrogen rich gas. One of the main issues of the reformer engine is the effects of reformate gas components on combustion performance. To clarify the effect of reformate gas contents on combustion stability, chemical kinetic simulations and single-cylinder engine test, in which hydrogen, CO, methane and simulated gas were added to intake air, were executed. And it is confirmed that hydrogen additive rate is dominant on high EGR combustion. The other issue to realize the fuel reformer was the catalyst deterioration. Catalyst reforming and exposure test were carried out to understand the influence of actual exhaust gas on the catalyst performance.

Fuel economy can be improved by reducing engine displacement, thanks to the resulting smaller friction losses and pumping losses. However, smaller engines frequently operate at high-engine speed and high-load, when pressure on the accelerator increases during acceleration and at high speed. To protect exhaust system components from thermal stress, exhaust gas temperature is reduced by fuel enrichment. To improve fuel economy, it is important to increase the frequency of stoichiometric operation at high-engine speed and high-load. Usually, the start timing of fuel enrichment is based upon temperature requirements to protect the catalyst. In the high-engine speed and high-load zone, the threshold temperature of catalyst protection is attained after some time because of the heat mass. Therefore, stoichiometric operation can be maintained until the catalyst temperature reaches the threshold temperature.

In 2006, Nissan began limited leasing of the X-TRAIL FCV equipped with their in-house developed Fuel Cell (FC) stack. Since then, the FC stack has been improved in durability, cold start-up capability, cost and size with the aim of promoting full-scale commercialization of FCVs. However, reduction of cost and size has remained a significant challenge because limited mass transport through the membrane electrode assembly (MEA) has made it difficult to increase the rated current density of the FC. Furthermore, it has been difficult to reduce the variety of FC stack components due to the complex stack configuration. In this study, improvements have been achieved mainly by adopting an advanced MEA to overcome these difficulties. First, the adoption of a new MEA and separators has improved mass transport through the MEA for increased rated current density. Second, an integrated molded frame (IMF) has been adopted as the MEA support.

In 2006, Nissan began limited leasing of the X-TRAIL FCV equipped with their in-house developed Fuel Cell (FC) stack. Since then, the FC stack has been improved in cost, size, durability and cold start-up capability with the aim of promoting full-scale commercialization of FCVs. However, reduction of cost and size has remained a significant challenge because limited mass transport through the membrane electrode assembly (MEA) has made it difficult to increase the rated current density of the FC. Furthermore, it has been difficult to reduce the variety of FC stack components due to the complex stack configuration. In this study, improvements have been achieved mainly by adopting an advanced MEA to overcome these difficulties. First, the adoption of a new MEA and separators has improved mass transport through the MEA for increased rated current density. Second, an integrated molded frame (IMF) has been adopted as the MEA support.

In recent years, catalyst systems such as a lean NOx trap (LNT) catalyst system and a urea selective catalytic reduction (SCR) system have been developed to obtain cleaner diesel emissions. At Nissan, we developed an emission control system for meeting Tier 2 Bin 5 requirements in 2003. On the basis of that technology, a new HC-NOx trap catalyst system has now been developed that complies with the SULEV standards without increasing the catalyst volume and precious metal loading. Compliance with the SULEV standards requires a further reduction of HC (NMHC) emissions by 84% and NOx by 60% compared with the emission performance Tier 2 Bin 5 compliant catalyst system. Consequently high conversion performance for both HCs and NOx is needed. An investigation of HC emission behavior under the FTP75 mode showed that a reduction of cold-phase HCs was critical for meeting the standard. Large quantities of HCs above C4 are emitted in the cold state.

Since the stable operating region of a gasoline-fueled HCCI engine is limited to the part load condition, a mode change between SI and HCCI combustion is required, which poses an issue due to the difference in combustion characteristics. This report focuses on the combustion characteristics in the transitional range. The combustion mode in the transitional range is investigated by varying the internal EGR rate, intake air pressure, and spark advance timing in steady-state experiments. In this parametric study, stable SI-CI combustion is observed. This indicates that the combustion mode transition is possible without misfiring or knocking, regardless of the speed of variable valve mechanism which includes VVA, VVEL, VTEC, VVL and so on, though the response of intake air pressure still remains as a subject to be examined in the actual application.

In order to clarify future automobile technologies and fuel qualities to improve air quality, second phase of Japan Clean Air Program (JCAPII) had been conducted from 2002 to 2007. Predicting improvement in air quality that might be attained by introducing new emission control technologies and determining fuel qualities required for the technologies is one of the main issues of this program. Unregulated material WG of JCAPII had studied unregulated emissions from gasoline and diesel engines. Eight gaseous hydrocarbons (HC), four Aldehydes and three polycyclic aromatic hydrocarbons (PAHs) were evaluated as unregulated emissions. Specifically, emissions of the following components were measured: 1,3-Butadiene, Benzene, Toluene, Xylene, Ethylbenzene, 1,3,5-Trimethyl-benzene, n-Hexane, Styrene as gaseous HCs, Formaldehyde, Acetaldehyde, Acrolein, Benzaldehyde as Aldehydes, and Benzo(a)pyrene, Benzo(b)fluoranthene, Benzo(k)fluoranthene as PAHs.

Some automakers have been studying variable compression ratio (VCR) technology as one possible way of improving fuel economy. In previous studies, we have developed a VCR mechanism of a unique multiple-link configuration that achieves a piston stroke characterized by semi-sinusoidal oscillation and lower piston acceleration at top dead center than on conventional mechanisms. By controlling compression ratio with this multiple-link VCR mechanism so that it optimally matches any operating condition, the mechanism has demonstrated that both lower fuel consumption and higher output power are simultaneously possible. However, it has also been observed that fuel consumption does not reduce further once the compression ratio reached a certain level. This study focused on the fact that the piston-stroke characteristic obtained with the multiple-link mechanism is suitable to a longer stroke.

The purpose of this study is to clarify the state of heat loss to the cylinder liner of the tested engine of which piston and cylinder head were previously measured. The authors' group developed an original measurement technique of instantaneous surface temperature at the cylinder liner wall using thin-film thermocouples. The temperature was measured at 36 points in total. The instantaneous heat flux was calculated by heat transfer analysis using measurement results of the temperature at the wall. As a result, the heat loss ratio to all combustion chamber walls is evaluated except the intake and exhaust valves.

Three-dimensional combustion simulation tools together with the Universal Coherent Flamelet Model (UCFM), a flame propagation model, have been applied to SI lean-burn combustion to study the influence of the equivalence ratio on the amount of unburned hydrocarbons (HCs). Unburned HCs from piston-cylinder crevices were taken into the consideration by using a calculation grid incorporating the actual crevice volume and shape and by applying an autoignition model to post-flame phenomena. The calculation results show the general tendencies for the total amount of unburned HCs and their distribution in the combustion chamber.

Nissan Motor has put on the European SUV market a 2.2-L direct-injection diesel engine with a diesel particulate filter (DPF) system that complies with the EURO IV emission regulations. This paper describes the DPF system, cooperative control of a variable geometry turbo (VGT) and exhaust gas recirculation (EGR), and a high-accuracy lambda control adopted for this engine. In order to achieve a compact DPF, the high-accuracy lambda control was developed to reduce variation in engine-out particulate matter (PM) emissions. Moreover, the accuracy of the technique for predicting the quantity of PM accumulation was improved for reliable detection of the DPF regeneration. Prediction error for PM accumulation increases during transient operation. Control logic was adopted to correct the PM prediction according to lambda fluctuation detected by an observer for lambda at cylinder under transient operating conditions. The observer is corrected lambda sensor output.

In the Japan Clean Air Program II (JCAP II) Diesel WG, effects of fuel properties on the performance of two types of diesel NOx emission aftertreatment devices, a Urea-SCR system and a NOx storage reduction (NSR) catalyst system, were examined. For a Urea-SCR system, the NOx emission reduction performance with and without an oxidation catalyst installed in front of the SCR catalyst at low exhaust gas temperature operation was compared. For an NSR catalyst system, the effect of fuel sulfur on both emissions and fuel economy during 50,000 km driving was examined. Furthermore, effects of other fuel properties such as distillation on exhaust emissions were investigated. The results show that sulfur is the influential factor for both devices. Namely, high NOx emission reduction performance of the Urea-SCR system with the oxidation catalyst at low exhaust gas temperature operation is influenced by sulfur.

Emission regulations for diesel-powered vehicles have been gradually tightening. Installation of after-treatment devices such as diesel particulate filters (DPF), NOx storage reduction (NSR) catalysts, and so on is indispensable to satisfy rigorous limits of particulate matter (PM) and nitrogen oxides (NOx). Japan Clean Air Program II Oil Working Group (JCAPII Oil WG) has been investigating the effect of engine oil on advanced diesel after-treatment devices. First of all, we researched the impact of oil-derived ash on continuous regeneration-type diesel particulate filter (CR-DPF), and already reported that the less sulfated ash in oil gave rise to lower pressure drop across CR-DPF [1]. In this paper, impact of oil-derived sulfur and phosphorus on NSR catalyst was investigated using a 4L direct injection common-rail diesel engine with turbo-intercooler. This engine equipped with NSR catalyst meets the Japanese new short-term emission regulations.

This paper presents a measurement technique to visualize the distribution of the in-cylinder mixture temperature and an experimental approach for analyzing the effect of the temperature distribution prior to ignition on homogeneous charge compression ignition (HCCI) combustion. First, a visualization technique for mixture temperature distribution based on the temperature dependence of laser induced fluorescence (LIF) was developed. As the next step, measurement of the temperature distribution was applied to an analysis of HCCI combustion. Controlled non-uniform temperature distributions in the mixture prior to ignition were generated by a special intake system with a completely divided intake port having separate electrical heaters.

Vehicle manufacturers developed two mixture formation concepts for the first generation of gasoline direct-injection (GDI) engines. Both the wall-guided concept with reverse tumble air motion or swirl air motion and the air-guided concept with tumble air motion have the fuel injector located at the side of the combustion chamber between the two intake ports. This paper proposes a new GDI concept. It has the fuel injector located at almost the center of the combustion chamber and with the spark plug positioned nearby. An oval bowl is provided in the piston crown. The fuel spray is injected at high fuel pressures of up to 100 MPa. The spray creates strong air motion in the combustion chamber and reaches the piston bowl. The wall of the piston bowl changes the direction of the spray and air motion, producing an upward flow. The spray and air flow rise and reach the spark plug.

A transient knock prediction technique has been developed by coupling a zero-dimensional knocking simulation with chemical kinetics and a one-dimensional gas exchange engine model to study the occurrence of transient knock in SI engines. A mixed chemical reaction mechanism of the primary reference fuels was implemented in the two-zone combustion chamber model as the auto-ignition model of the end-gas. An empirical correlation between end-gas auto-ignition and knock intensity obtained through intensive analysis of experimental data has been applied to the knocking simulation with the aim of obtaining better prediction accuracy. The results of calculations made under various engine operating parameters show good agreement with experimental data for trace knock sensitivity to spark advance.