Search Results

Mo-free 1.6-GPa bolt was developed for a Variable Compression Turbo (VC-Turbo) engine, which is environment friendly and improves fuel efficiency and output. Mo contributes to the improvement of delayed fracture resistance; therefore, the main objective is to achieve both high strength and delayed fracture resistance. Therefore, Si is added to the developed steel to achieve high strength and delayed fracture resistance. The delayed fracture tests were performed employing the Hc/He method. Hc is the limit of the diffusible hydrogen content without causing a delayed fracture under tightening, and He is the diffusible hydrogen content entering under a hydrogen-charging condition equivalent to the actual environment. The delayed fracture resistance is compared between the developed steel and the SCM440 utilized for 1.2-GPa class bolt as a representative of the current high-strength bolts.

The size and weight of the traction inverter needs to be reduced to ensure a sufficient cruising range of an electric vehicle. To this end, one approach involves changing materials of the inverter case from aluminum to resin. However, the resin in use of inverter case causes technical issues in terms of collision performance, electromagnetic compatibility (EMC), and cooling performance because of the difference in the material properties between the resin and the conventionally used aluminum. By solving the abovementioned issues, a resin water jacket case (hereinafter, resin water jacket) was successfully adopted with inverters designed for next-generation electric powertrain in mass production models for the first time. The resin-based structure had advantages to reduce the weight of the inverter case by ~35% and decrease the number of parts to ~3/5, compared to that for the conventional cases.

Prediction of the discharge path behavior between electrodes on a spark plug is important for efficient energy use in internal combustion engines, especially in lean combustion. In this paper, we propose a numerical model for the prediction of the spark path behaviors based on the coupling of a flow field, a Lagrangian particle model, and an equivalent circuit model. A turbulent flow around cylinders imitating electrodes is solved using a direct numerical simulation, in which Lagrangian particles along the spark path are tracked. Electric current and inter-electrode voltage are computed based on the energy conversion rate from the circuit to the mixture gas. As a result, a discharge path is reproduced with Lagrangian tracking particles virtually aligned between the cylinders. The spark path has a complicated structure along the spanwise direction due to the complex three-dimensional vortical structure of the cylinder wake.

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.

Engine oil with viscosity lower than 0W-16 has been needed for improving fuel efficiency in the Japanese market. However, lower viscosity oil generally has negative aspects with regard to oil consumption and anti-wear performance. The technical challenges are to reduce viscosity while keeping anti-wear performance and volatility level the same as 0W-20 oil. They have been solved in developing a new engine oil by focusing on the molybdenum dithiocarbamate friction modifier and base oil properties. This paper describes the new oil that supports good fuel efficiency while reliably maintaining other necessary performance attributes.

The octane appetite of an engine is frequently characterised by the so-called K value. It is usually assumed that K is dependent only on the thermodynamic conditions in the engine when knock occurs. In this work we test this hypothesis: further analysis was conducted on experimental results from SAE 2019-01-0035 in which a matrix of fuels was tested in a single cylinder engine. The fuels consisted of a relatively small number of components, thereby simplifying the analysis of the chemical kinetic proprieties. Through dividing the original fuel matrix into subsets, it was possible to explore the variation of K value with fuel properties. It was found that K value tends to increase slightly with RON. The explanation for this finding is that higher RON leads to advanced ignition timing (i.e. closer to MBT conditions) and advanced ignition timing results in faster combustion because of the higher pressures and temperatures reached in the thermodynamic trajectory.

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.

The thermal efficiency of internal combustion engines can be improved dramatically with the right combination of engine technology and fuel technology. Super lean-burn technology is attracting attention as a means of boosting thermal efficiency. However, there is a limit to how lean a fuel-air mixture can be before combustion becomes unstable or misfire occurs. The authors evaluated the effects of various chemical compositions on the lean limit under super lean-burn conditions. By changing the composition of the fuel, it was possible to achieve excess air ratios of over 2.0, resulting in high thermal efficiency.

In order to improve the accuracy of the coil temperature prediction, detailed fundamental experiments have been conducted on thermal resistances that are caused by the void air gap and contact surfaces. The thermal resistance of the coil around the air gap can be calculated by an air gap distance and air heat conductivity. Contact surface thermal resistance between the core and the housing was constant regardless of the press-fitting state in this experiment. Prediction accuracy of the coil temperature is improved by including the heat resistance characteristics that is obtained by the basic experiment to conjugate heat transfer analysis model.

A new variable compression turbo (VC-Turbo) engine, which has a multi-link system for controlling the compression ratio from 8:1 to 14:1, requires high axial force for fastening the multi-links because of high input loads and the downsizing requirement. Therefore, it was necessary to develop a 1.6-GPa tensile strength bolt with plastic region tightening. One of the biggest technical concerns is delayed fracture. In this study, quenched and tempered alloy steels were chosen for the 1.6-GPa tensile strength bolt.

To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods.

An electric vehicle (EV) has less powertrain energy loss than an internal combustion engine vehicle (ICE), so its aerodynamic accounts have a larger portion of drag contribution of the total energy loss. This means that EV aerodynamic performance has a larger impact on the all-electric range (AER). Therefore, the target set for the aerodynamics development for a new EV hatchback was to improving AER for the customer’s benefit. To achieve lower aerodynamic drag than the previous model’s good aerodynamic performance, an ideal airflow wake structure was initially defined for the new EV hatchback that has a flat underbody with no exhaust system. Several important parameters were specified and proper numerical values for the ideal airflow were defined for them. As a result, the new EV hatchback achieves a 4% reduction in drag coefficient (CD) from the previous model.

A new 2L gasoline turbo engine, named KR20DDET was developed with the world’s first mass-producible variable compression turbo (VC-Turbo) technology using a multi-link variable compression ratio (VCR) mechanism. It is well known that increasing the compression ratio improves gasoline engine thermal efficiency. However, there has always been a compromise for engine designers because of the trade-off between increasing the compression ratio and knocking. At Nissan we have been working on VCR technology for more than 20 years and have now successfully applied this technology to a mass production engine. This technology uses a multi-link mechanism to change the top and bottom dead center positions, thereby allowing the compression ratio to be continuously changed. The VC-Turbo engine with this technology can vary the compression ratio from 14:1 for obtaining high thermal efficiency to 8:1 for delivering high torque by taking advantage of the strong synergy with turbocharging.

It has been shown that lean burn is effective for improving the thermal efficiency of gasoline SI engines. This happens because the reduction of heat loss by decrease of flame temperature. On the other hand, the fuel dilution of the premixed gas makes the combustion speed low, and cycle-to-cycle variations of combustion are increased by excessive dilution, it is difficult to increase the thermal efficiency of the gasoline SI engine. Influence of ignition by spark discharge is considered as a factor of combustion variation, and it is necessary to understand the effects of spark discharge characteristics on the lean combustion process. Spark discharge in the SI engines supplies energy to the premixed-gas via a discharge channel in the spark plug gap which ignites the premixed-gas. The discharge channel is elongated by in-cylinder gas flow and its behavior varies in each cycles.

Super lean burn technology is conceived as one of methods for improving the thermal efficiency of SI engines[1][2]. For lean burn, reduction of heat loss and the due to decrease in flame temperature can be expected. However, as the premixed gas dilutes, the combustion speed decreases, so the combustion fluctuation between cycles increases. Also, to improve the thermal efficiency, the ignition timing is advanced to advance the combustion phase. However, when the combustion phase is excessively advanced, knocking occurs, which hinders the improvement of thermal efficiency. Knocking is a phenomenon in which unburned gas in a combustion chamber compressed by a piston and combustion gas suffer compression auto-ignition. It is necessary to avoid knocking because the amplitude of the large pressure wave may cause noise and damage to the engine. Also, knocking is not a steady phenomenon but a phenomenon that fluctuates from cycle to cycle.

Improving the thermal efficiency of spark ignition (SI) engine is strongly required due to its widespread use but considerably less efficiency than that of compression ignition (CI) engine. Although lean SI engine operation can offer substantial improvements of the thermal efficiency relative to that of traditional stoichiometric SI operation, the cycle-to-cycle variations of combustion increases with the level of air dilution, and becomes unacceptable. To improve the stability of lean operation, this study examines the effects of spark discharge pattern and tumble level on cycle-to-cycle variations of combustion at lean limits. The spark discharge pattern was altered by a custom inductive ignition system using ten spark coils and the tumble level was increased by a custom adapter installed in the intake port (tumble adapter).

A low viscosity API SN 0W-16 engine oil was developed to achieve a 0.5% improvement in fuel efficiency over the current GF-5/API SN 0W-20 oil. Oil consumption and engine wear are the main roadblocks to the development of low viscosity engine oils. However, optimization of the base oil and additives successfully prevent oil consumption and wear. First, it was confirmed in engine tests that NOACK volatility is still an effective indicator of oil consumption even for a low viscosity grade like 0W-16. As a result of base oil volatility control, the newly developed oil achieves the same level of oil consumption as the current GF-5/API SN 0W-20 oil. Second, it was found that the base oil viscosity and molybdenum dithiocarbamate (MoDTC) had a significant effect on chain wear in rig testing that simulated silent chain wear. For the same base oil viscosity, the new oil maintains the same oil film thickness under high surface pressure.

The effects of lubricant oil and fuel properties on low speed pre-ignition (LSPI) occurrence in boosted S.I. engines were experimentally evaluated with multi-cylinder engine and de-correlated oil and fuel matrices. Further, the auto-ignitability of fuel spray droplets and evaporated homogeneous fuel/oil mixtures were evaluated in a combustion bomb and pressure differential scanning calorimetry (PDSC) tests to analyze the fundamental ignition process. The work investigated the effect of engine conditions, fuel volatility and various lubricant additives on LSPI occurrence. The results support the validity of aspects of the LSPI mechanism hypothesis based on the phenomenon of droplets of lubricant oil/fuel mixture (caused by adhesion of fuel spray on the liner wall) flying into the chamber and autoigniting before spark ignition.

With the development of downsized spark ignition (SI) engines, low-speed pre-ignition (LSPI) has been observed more frequently as an abnormal combustion phenomenon, and there is a critical need to solve this issue. It has been acknowledged that LSPI is not directly triggered by autoignition of the fuel, but by some other material with a short ignition delay time. It was previously reported that LSPI can be caused by droplets of lubricant oil intermixed with the fuel. In this work, the ignition behavior of lubricant component containing fuel droplets was experimentally investigated by using a constant volume chamber (CVC) and a rapid compression and expansion machine (RCEM), which enable visualization of the combustion process in the cylinder. Various combinations of fuel compositions for the ambient fuel-air mixture and fractions of base oil/metallic additives/fuel for droplets were tested.

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.