Tomonori Urushihara

A Study of a Gasoline-fueled Compression Ignition Engine ∼ Expansion of HCCI Operation Range Using SI Combustion as a Trigger of Compression Ignition ∼

A new combustion concept, called spark-ignited compression ignition (SI-CI) combustion, is proposed for expanding the operation range of homogeneous charge compression ignition (HCCI) combustion. The authors previously showed that raising the mixture temperature before compression so as to induce auto-ignition near top dead center reduces the quantity of trapped gas, resulting in a lower maximum indicated mean effective pressure (IMEP). With the newly proposed combustion concept, auto-ignition of a homogeneous lean mixture is accomplished by the additional compression resulting from Sl combustion of a small quantity of stratified mixture instead of raising the intake air temperature. This SI-CI combustion process reduced the necessary increase in intake air temperature compared with conventional HCCI combustion. A higher maximum IMEP was achieved with SI-CI combustion than with conventional HCCI combustion, as was planned. However, nitrogen oxide (NOx) emissions increased due to the Sl portion of the combustion process. Reducing NOx emissions through the application of exhaust gas recirculation is an issue of SI-CI combustion for future research.

A trial of ignition innovation of gasoline engine by nanosecond pulsed low temperature plasma ignition

Application of nanosecond pulsed low temperature plasma as an ignition technique for automotive gasoline engines, which require a discharge under conditions of high back pressure, has been studied experimentally using a single-cylinder engine. The nanosecond pulsed plasma refers to the transient (non-equilibrated) phase of a plasma before the formation of an arc discharge; it was obtained by applying a high voltage with a nanosecond pulse (FWHM of approximately 80 or 25 ns) between coaxial cylindrical electrodes. It was confirmed that nanosecond pulsed plasma can form a volumetric multi-channel streamer discharge at an energy consumption of 60 mJ cycle−1 under a high back pressure of 1400 kPa. It was found that the initial combustion period was shortened compared with the conventional spark ignition. The initial flame visualization suggested that the nanosecond pulsed plasma ignition results in the formation of a spatially dispersed initial flame kernel at a position of high electric field strength around the central electrode. It was observed that the electric field strength in the air gap between the coaxial cylindrical electrodes was increased further by applying a shorter pulse. It was also clarified that the shorter pulse improved ignitability even further.

Turbulence and Cycle-by-Cycle Variation of Mean Velocity Generated by Swirl and Tumble Flow and Their Effects on Combustion

Combinations of swirl flow and tumble flow generated by 13 types of Swirl Control Valves were tested using both an impulse swirl meter and LDV. The LDV used in this study was developed especially for engine research to realize stable beam crossing at very narrow beam waists to achieve high spatial resolution measurement. It is shown that tumble flow generates turbulence in the combustion chamber more effectively than swirl flow, and that swirl reduces the cycle variation of mean velocity in the combustion chamber. Performance tests are also carried out to determine the combustion characteristics under the condition of homogeneous charge. Tumble flow promotes combustion to a greater extent than expected from its turbulence intensity. It is also shown that the lean-limit air/fuel ratio is not strongly related to cycle variation of mean velocity but to turbulence intensity.

Study of antiknock performance under various octane numbers and compression ratios in a DISI engine

This paper presents a study of antiknock performance under various octane numbers and compression ratios in a direct injection spark ignition (DISI) gasoline engine. The relationship between the octane number and engine performance in the DISI engine-the engine torque and the break specific fuel consumption (BSFC)-was investigated in comparison with a multipoint injection (MPI) engine. Due to the improvement in the charging efficiency and the advance of the ignition timing by cooled aspiration, the engine torque of the DISI engine was improved over that of the MPI engine. It was also found that the octane number requirement (ONR) was reduced. In addition, the possibility of engine performance enhancement at high compression ratios was studied. At high compression ratios, the engine torque is reduced due to the heavy knocking when low octane gasoline is used. However, an improvement in the engine torque has been observed with high octane gasoline. An increase in the ONR at a high compression ratio (15.0:1) was observed in both DISI and MPI engines, but the increase in the ONR in the DISI engine was smaller than in the MPI engine. The BSFC got worse under low-speed, high-load conditions at high compression ratios for retardation due to heavy knocking, while the BSFC was improved at low-speed, low-load and at middle speed for better thermal efficiency at high compression ratios. Finally, the benefits for fuel economy with high compression ratios and high octane gasolines were evaluated using J10-15, ECE-EUDC and LA-4 mode simulations.

Effects of swirl and tumble motion on fuel vapor behavior and mixture stratification in lean burn engine

Abstract Flow measurements using LDV and in-cylinder fuel vapor visualization using LIF (Laser Induced Fluorescence) were performed for various types of intake systems that generated several different combinations of swirl ratio and tumble ratio in the cylinder. The measured results indicate that there is a necessary condition for swirl ratio and tumble ratio to realize the charge stratification in the cylinder. Performance tests were also carried out to determine the combustion characteristics of each intake system. The features of combustion when the charge stratification was realized were analyzed.

A Study of Air-Fuel Mixture Formation in Direct-Injection SI Engines

An investigation was made into two approaches to air-fuel mixture formation in direct injection Sl engines in which charge stratification is controlled by swirl or tumble gas motions, respectively. Particle image velocimetry (PIV), laser-induced fluorescence (LIF) and air-fuel ratio measurement by infrared absorption were used to analyze fuel transport from the fuel injector to the spark plug and the fuel vaporization process. The results obtained were then compared with measured date as to combustion stability. As a result, the reason why the effects of injection timing on combustion stability were different between the two approaches was made clear from the standpoint of the mixture formation process.

Development of a technique for quantifying in-cylinder A/F ratio distribution using LIF image processing

Abstract Mixture formation in the cylinder greatly influences combustion. In this study, a system was developed for analyzing mixture formation by using LIF to visualize the formation process and image processing to quantify the air/fuel ratio distribution. Iso-octane was used as the fuel, DMA as the fluorescent tracer and a KrF excimer laser (wavelength of 248 nm) as the excitation light source. This system was used to visualize mixture formation in an engine with a tumble-type swirl control valve, and the effect of varying the fuel injection timing on mixture behavior and the A/F ratio distribution was examined.

A Study of a DISI Engine with a Centrally Located High-pressure Fuel Injector

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. The fuel injection pressure, the spray shape and the piston bowl geometry are important factors for the performance of stratified combustion with this concept.

LDA measurement and a theoretical analysis of the in-cylinder air motion in a DI diesel engine

The swirl velocity in the combustion bowl of a DI diesel engine was measured by means of laser doppler anemometry, varying the swirl intensity and engine speed. At the same time an axisymmetrical two dimensional laminar model for simulating the in-cylinder air motion was presented. The boundary condition of the flow near the wall was investigated by a comparison of predicted and measured swirl velocity, and as a result the free slip condition was found to be suitable for the present model.

Study of High Load Operation Limit Expansion for Gasoline Compression Ignition Engines

In this research, combustion characteristics of gasoline compression ignition engines have been analyzed numerically and experimentally with the aim of expanding the high load operation limit. The mechanism limiting high load operation under homogeneous charge compression ignition (HCCI) combustion was clarified. It was confirmed that retarding the combustion timing from top dead center (TDC) is an effective way to prevent knocking. However, with retarded combustion, combustion timing is substantially influenced by cycle-to-cycle variation of in-cylinder conditions. Therefore, an ignition timing control method is required to achieve stable retarded combustion. Using numerical analysis, it was found that ignition timing control could be achieved by creating a fuel-rich zone at the center of the cylinder. The fuel-rich zone works as an ignition source to ignite the surrounding fuel-lean zone. In this way, combustion consists of two separate auto-ignitions and is thus called two-step combustion. In the simulation, the high load operation limit was expanded using two-step combustion. An engine system identical to a direct-injection gasoline (DIG) engine was then used to demonstrate two-step combustion experimentally. An air-fuel distribution was created by splitting fuel injection into first and second injections. The spark plug was used to ignite the first combustion. This combustion process might better be called spark-ignited compression ignition combustion (SI-CI combustion). Using the spark plug, stable two-step combustion was achieved, thereby demonstrating a means of expanding the operation limit of gasoline compression ignition engines toward a higher load range.Copyright