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Observations of the scavenging flow field have been made in a modified poppet-valved two-stroke engine with a transparent cylinder. Four kinds of cylinder heads with different port configuration were created to analyze their effects on the scavenging flow and develop new scavenging concepts. A mineral oil fog discharge system was used to visualize the air flow during the scavenging process. All of the images were recorded by a high speed video camera which show the development of the scavenging processes and clearly indicate the scavenging jet structure, the tumble pattern and the location of re-circulation regions. The analyses allow us to judge the quality of the scavenging processes. The small changes in port geometry could significantly affect the scavenging flow. Tumble as well as swirl should be considered as main means to organize the scavenging flow in order to avoid short-circuiting losses and create condition favorable to combustion.

Performance of a CNG (Compressed natural gas) two stroke cycle S.I. engine using intermittent low pressure fuel injection from scavenging ports is investigated experimentally. The test engine is a two cylinder, 398 cm3, two stroke cycle spark ignition engine. Gaseous fuel injectors are attached at the engine block, and a CNG is injected into the scavenging passage through a fuel injection pipe. The fuel injection pressure is set at 0.255 MPa, and the fuel is injected intermittently during the scavenging process. The length and tip geometry of the fuel injection pipe are varied, and the effect on the engine performance is investigated. Using the scavenging port fuel injection, the BSFC is reduced by 25 %, and the lean burn limit extends from λ = 1.2 to 1.46, at the maximum. The peak of the NOx emission shifts to leaner side, and the THC emission is reduced by 47 % at the maximum.

An experimental study on a direct-injection gasoline spray initiated from a swirl injector was carried out in order to clarify the effects of ambient temperature and pressure. The sprays were formed in a pressure chamber where the maximum pressure and temperature reached 1.1 MPa and 423 K respectively. The spray-tip penetration for elevated ambient temperature is slightly longer than that for normal ambient temperature. From the measurement using phase Doppler anemometry, it was found that the Sauter mean diameter D32 is large under high ambient pressure condition. The effect of elevating the ambient temperature is to decrease D32 in the core region of the spray.

This paper presents further investigation into the effects of using biomass oil-diesel fuel blends on the characteristics of operation and emissions in a production DI diesel engine. Neat coconut oil was chosen in terms of its beneficial property of chemical stability and agricultural productivity. The spray characteristics were evaluated with a phase doppler anemometer. Operation of the test engine was shown to be successful even without any engine modification. Results show that neat coconut oil operation gave lower smoke and NOx emissions. The mechanism of these effects are discussed.

There have been many experiments to characterize Diesel fuel spray under steady-state conditions. However, the best number and position of holes on the sac to be used in the experiment are not clear. To address these question, we investigate Diesel type spray flows using a laser Doppler anemometer (LDA) and a phase Doppler anemometer (PDA). Spray flow characteristics, such as mean and fluctuating two component velocities, the two dimensional distribution of particle diameter and the three parameter variation at the log-hyperbolic fitting according to particle size distribution, are given from measured data. Spray jets from four varieties of Diesel nozzle are compared with each other to identify the differences in spray characteristics between them. The results show that the spray from the original single-hole nozzle on the top of the sac is distinct from the other types of nozzle.

This paper presents basic combustion behavior of a compressed natural gas directly injected into a cylinder with spark-ignition. Experiments were conducted in a rapid-compression machine (RCM) with the cylinder bore of 80 mm, the stroke of 180 mm and the compression ratio of 10 at TDC. A CNG was injected through specially designed injectors which were installed at the side of combustion chamber with three modes, twin injectors in parallel, twin injectors in opposed and single injector. Combustion products were also measured with an infra-red gas analyzer. Direct photographs were taken with a high-speed video for observation. Effect of fuel injection timing was examined at constant spark timing together with the influence of injection mode. Results show several beneficial combustion characteristics of direct injection combustion using CNG. Combining with the results of combustion products and photographic observation, the combustion mechanism is discussed.

Characteristics of compressed natural gas (CNG) direct injection auto-ignition were investigated experimentally. A rapid compression machine (RCM) with the compression ratio of 10 was used. The diameter and thickness of the combustion chamber are 80 mm and 20 mm, respectively. After the compression start, fuel was directly injected with a single hole injector at the injection pressure of 7.0 MPa, and auto-ignition takes place. The fuel injection timing was varied from 50 ms to 60 ms from the compression start. Two kinds of natural gasses were tested; 12A (CH4: 99.1 %) and 13A (CH4: 86.3 %, C2H6: 5.2 %, C3H8: 1.9 % and others). A glow plug was installed in the cylinder in order to assist the ignition, which was set at 30 mm downstream from the fuel injector nozzle exit. Two kinds of auto-ignition processes were observed. For CNG 12A, auto-ignition always takes place after the end of the fuel injection. The ignition delay is relatively long (40 to 80 ms) and the fluctuation is large.

Three-dimensional computations are performed to investigate the scavenging characteristics of poppet-valved two-stroke engines. The new subroutines are developed to handle various valve shrouds. Visualization of scavenging flow on a modified two-stroke transparent cylinder engine is used for validation and compared well in flow pattern. The flows in engines with different configurations are simulated at a speed of 5000 r/min. The stroke bore/ratio and valve arrangements were considered to investigate their effects on the scavenging flows. Additionally, valve timing and boost pressure have also been studied. The results show that stroke/bore ratio of 0.4 to 0.6, shroud angle of 69° to 108°, turn angle of shroud of 18° to 28°, average tumble ratio of 1.2-1.6 were found to be the optimum range for effective scavenging.

Velocity measurement of an intermittent high-speed flow inside a micro wave rotor cell was carried out using a laser Doppler anemometry (LDA). The cell is 3 × 3 mm rectangular tube, whose length is 42 mm. The pressure ratio and rotor speed of the wave rotor were set at 2.5 and 5,000 rpm, respectively. Ethanol droplets were seeded into the flow as scattering particles. By use of laser beam expanders, the probe volume of the LDA optics was minimized, and sub-millimeter special resolution is realized while a wide velocity range (-100 to 300 m/s) is kept. It is shown that the velocity histories at local positions inside the wave rotor cell can be obtained with the LDA optics. The rapid velocity increase and decrease, due to the primary and secondary shock waves, are observed, and the propagation speed of the shock waves was estimated. It is shown that the velocity profile inside the cell is flat and that the boundary layer thickness inside the cell is smaller than 0.5 mm.

This paper presents the effect of application of scavenging-port injection to a two-stroke two-cylinder boat engine fueled with a compressed natural gas (CNG). Experiments were carried out at a constant speed of 3000 rpm and WOT condition with varying excess air ratio in lean region. A CNG injector for a production automobile engine was utilized and installed into the scavenging ports. Comparison was made with homogeneous charge operation using a gas mixer. By applying the scavenging-port injection, unburned-fuel in the exhaust gas was reduced close to half which must be due to the reduction of fuel short-cutting during the gas exchange process. The lean-burn limit was extended from the excess air ratio of 1.21 to 1.57. The maximum decrease of BSFC reached to 25 %. This suggests that stratified-combustion could be realized in its lean-burn region.

The most serious problem in a 2-stroke spark-ignition engine is poor trapping of fresh charge. To solve this problem, a scavenging-port injection was applied, and a fuel injection pipe (FIP) was installed at the injector tip. In a previous study, it was shown that the BSFC and emission characteristics were drastically improved. In the present study, effect of increase in the fuel injection rate was investigated. It is shown that the BSFC and the THC emissions improved at high engine speeds, while they slightly deteriorate at low engine speeds. The increase in the fuel injection rate is effective particularly at high engine speeds, where the scavenging duration becomes shorter.

Effects of horn geometry on the atomization characteristics of an ultrasonic fuel injector using a micro nozzle array were investigated experimentally. Micro nozzles whose exit diameter d = 3 μm are mounted on a thin metal film. The number of the micro nozzles is from 2.0 × 104 to 1.2 × 105. Using an ultrasonic oscillator, gasoline is periodically pushed out from the micro nozzles at a frequency from 62 to 65 kHz. A disk type PZT (Lead zirconium titanate) is used as an ultrasonic oscillator, and the oscillation is amplified using a step-type horn. The input voltage to the PZT is varied from 0 to 200 V. To increase the fuel flow rate, the horn small end diameter DS is increased from 10.5 to 25 mm, while the large end diameter is fixed at 30 mm. To prevent forming a liquid film on the micro nozzle array, gutters are machined on the small end of the horn. It is shown that the SMD (Sauter mean diameter) of the spray is almost uniform around 10 to 14 μm.