Search Results

The necessity of the reduction of the lubricating oil consumption of diesel engines has been increasing its importance to reduce the negative effect of exhausted oil on after treatment devices for exhausted gas. The final purpose of the studies is clarifying the mechanism of the oil consumption and developing the method of its estimation. For the basic study, the mechanism of oil film generation on the piston skirt could be explained by hydrodynamic lubrication in our first and second reports [1, 2]. In this paper, the piston skirt was calculated using the measured piston motion to clarify the effect of the piston motion to the piston skirt oil film behavior.

Clarifying the mechanism of the oil consumption of engines is necessary for developing its estimation method. Oil moves upwards on the piston to the combustion chamber through ring sliding surfaces, ring backs and ring gaps. The mechanisms of oil upwards transport through the ring gaps are hardly analyzed. In this report, oil pressure just under the oil ring was successfully measured by newly developed method to clarify the oil transport mechanism at the ring gap. It was showed that the generated oil pressure pushed up the oil at the ring gap.

The requirement for the reduction of lubricating oil consumption of diesel engines has become increasingly important in reducing the effect of exhausted oil on after treatment devices for exhaust gas. In our first report, findings indicated that piston skirt length affected oil consumption, and they clearly showed that the oil film on the piston skirt should be considered in the calculation for oil consumption. In this report, the mechanism of oil film generation on the piston skirt is investigated. The oil film on the piston skirt is calculated and the effect of piston motion on the oil film region is clarified, i.e., considering the piston rotation around the top of the piston skirt at the anti-thrust side is important for the calculation of the oil film region.

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.

In our previous reports, we proposed a new focusing engine with high thermal efficiency based on relatively-silent high compression and nearly-complete air-insulation effect, which employs pulsed multi-jets of gas collided around chamber center. Local compression level due to the gas jets colliding around chamber center before reaction can be varied from zero to 100MPa and 3000K, by changing the number of jets and intake pressure. Relatively-silent high compression is possible, because region around chamber wall is at pressure level of traditional engines. This is suitable for various usages of automobiles, aerocrafts, and rockets, and also for various fuels including hydrogen, because high compression around chamber center leads to stable auto-ignition and potential of low NOx at very lean burning operation. We developed two types of focusing compression engines, without and with piston. For the new engine without piston, we obtained nearly-complete air-insulation and high thrust.

A new engine concept (Fugine) based on colliding pulsed supermulti-jets was proposed in recent years, which is expected to provide high thermal efficiencies over 50% and less combustion noise. Theoretical analyses indicate a high potential for thermal efficiency over 60%. Three types of prototype engines have been developed. The first prototype engine based only on the colliding of pulsed supermulti-jets with fourteen nozzles has no piston compression, while the second type equipped with a low-cost gasoline injector in the suction port has a double piston system and eight jet nozzles. Combustion experiments conducted on the second prototype gasoline engine show high thermal efficiency similar to that of traditional diesel engines and lower combustion noise comparable to that of traditional spark-ignition gasoline engines.

This study examines the effects of ethanol content on engine performances and the knock characteristics in spark ignition gasoline engine under various compression ratio conditions by cylinder pressure analysis, visualization and numerical simulation. The results confirm that increasing the ethanol content provides for greater engine torque and thermal efficiency as a result of the improvement of knock tolerance. It was also confirmed that increasing the compression ratio together with increasing ethanol content is effective to overcome the shortcomings of poor fuel economy caused by the low calorific value of ethanol. Further, the results of one dimensional flame propagation simulation show that ethanol content increase laminar burning velocity. Moreover, the results of visualization by using a bore scope demonstrate that ethanol affects the increase of initial flame propagation speed and thus helps suppress knock.

Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline.

A single-point autoignition gasoline engine (Fugine) proposed by us previously has a strongly asymmetric double piston unit without poppet valves, in which pulsed multi-jets injected from eight suction nozzles collide around the combustion chamber center. Combustion experiments conducted on this engine at a low operating speed of 2000 rpm using gasoline as the test fuel under lean burn conditions showed both high thermal efficiency comparable to that of diesel engines and silent combustion comparable to that of conventional spark-ignition gasoline engines. This gasoline engine was tested with a weak level of point compression generated by negative pressure of about 0.04 MPa and also at an additional mechanical homogeneous compression ratio of about 8:1 without throttle valves. After single-point autoignition, turbulent flame propagation may occur at the later stage of heat release.

Natural gas is a promising alternative fuel for internal combustion engines because of its clean combustion characteristics and abundant reserves. However, it has several disadvantages due to its low energy density and low thermal efficiency at low loads. Thus, to assist efforts to improve the thermal efficiency of spark-ignited (SI) engines operating on natural gas and to minimize test procedures, a numerical simulation model was developed to predict and optimize the performance of a turbocharged test engine, considering flame propagation, occurrence of knock and ignition timing. The numerical results correlate well with empirical data, and show that increasing compression ratios and retarding the intake valve closing (IVC) timing relative to selected baseline conditions could effectively improve thermal efficiency. In addition, employing moderate EGR ratios is also effective for avoiding knock.

To suppress knock in small gasoline engines, the coolant flow of a single-cylinder engine was improved by using two methods: a multi-dimensional knock prediction method combining a Flamelet model with a simple chemical kinetics model, and a method for predicting combustion chamber wall temperature based on a thermal fluid calculation that coupled the engine coolant and the engine structure (engine head, cylinder block, and head gasket). Through these calculations as well as the measurement of wall temperatures and the analysis of combustion by experiments, the effects of wall temperature distribution and consequent unburnt gas temperature distribution on knock onset timing and location were examined. Furthermore, a study was made to develop a method for cooling the head side, which was more effective to suppress knock: the head gasket shape was modified to change the coolant flow and thereby improve the distribution of wall temperatures on the head side.

In our previous reports based on computations and fluid dynamic theory, we proposed a new compressive combustion principle for an inexpensive and relatively quiet engine reactor that has the potential to achieve thermal efficiency over 50% even for small combustion chambers having less than 100 cc. This can be achieved with colliding supermulti-jets that create complete air insulation to encase burned gas around the chamber center. We originally developed two small prototype engine systems for gasoline. First one with one rotary valve for pulsating intake flow and sixteen nozzles of jets colliding has no pistons. Next, we developed the second one having a strongly-asymmetric double piston system with the supermulti-jets colliding, although there are no poppet valves. The second prototype engine can vary point-compression strength due to the supermulti-jets and homogeneous compression level due to piston, by changing phase and size of two gears.