Search Results

A laser 2-focus velocimeter(L2F) has been utilized for the measurements of the velocity and size of droplets in diesel fuel sprays injected from a 6-hole nozzle. The fuel was stored once in a common rail and was injected intermittently to the atmosphere by using a solenoid injector. The diameter of the nozzle orifice was 0.165 mm. The injection pressure was 60 MPa. The injector solenoid was driven by the current having a waveform consisted of 3 stages; boot, pull, and hold. The injection amounts were set at 0.8, 2.9, 3.9 and 4.7mg by changing the durations of the pull stage and the hold stage. The L2F measurement was conducted at 10 mm downstream from the nozzle exit. The fluctuation intensity of the droplet velocity was found to be larger under the smaller injection amount. It was clearly shown that the arithmetic mean droplet size under the smaller injection amount was smaller than that under the larger injection amount during the hold current duration.

Measurements of temporal and spatial changes in the velocity and size of droplets of diesel fuel sprays under two injection pressures were conducted near the nozzle orifice by a laser 2-focus velocimeter (L2F). The result showed that the size of droplets under higher rail pressure was larger than that under lower rail pressure at the spray center and was smaller than that under lower rail pressure at the spray periphery. It was found that the size of droplets deceased in the downstream direction of the spray and the decrease rate increased with the rail pressure. The cross-sectional average velocity increased and the cross-sectional average size decreased with the rail pressure in the spray near the nozzle exit.

In order to utilize bio-alcohols as the fuel for diesel engines, combustion characteristics of alcohol blended with gas oil were compared between ethanol and n-butanol in a direct injection diesel engine. In the case of the same cetane number between ethanol and butanol blends, the time-history of combustion, in other words, the ignition delay, the diffusion combustion and the combustion duration, coincided almost completely in both blend fuels. However, the smoke density of the butanol blend was smaller than that of the ethanol blend. This result must be caused by difference in soot formation process between ethanol and butanol blends. Thus, it is difficult to predict the trend of the soot emission in combustion of alcohol blends only by using the existing phenomenological model of the soot formation in the combustion of gas oil.

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. Diesel fuel was injected intermittently into the atmosphere by using a 6-hole injector nozzle. The diameter of the nozzle orifice was 0.135mm. The injection pressure was set at 80MPa. Measurement positions were located at 5, 7, 10 and 15mm from the nozzle exit. The measurement result showed that the velocity of droplets at the spray center was the highest, and decreased in the direction towards the spray periphery. The size of droplets at the spray periphery was larger than the one at the spray center. The size of droplets decreased in the direction of droplet flight on the near nozzle plane. It is understood that the breakup of droplets occurred. The size of droplets increased in the direction of droplet flight at the spray periphery on downstream planes. It is understood that the coalescence of droplets occurred.

In order to realize a premixed compression ignition (PCI) engine by utilization of bio-alcohol, combustion characteristics of bio-alcohol blended with gas oil were compared between ethanol and n-butanol in a diesel engine. The effects of the ethanol blend ratio and the butanol blend ratio on ignition delay, premixed combustion, diffusion combustion, fuel consumption and exhaust emissions such as smoke density and NOx were investigated experimentally. It is found that ethanol almost burns out together with combustion of low evaporation temperature composition of gas oil in the premixed combustion period and the heat release in the diffusion combustion is based on mainly high evaporation temperature composition of gas oil, then, soot is formed in the diffusion combustion of gas oil. On the other hand, a part of butanol burns in the diffusion combustion, however, the combustion of butanol in the diffusion stage is not the cause of soot formation.

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. The focal diameter is about 3 μm, and the distance between two foci is 18 μm. The data acquisition rate of the L2F was increased to 15 MHz in order to capture every droplet appearing in the measurement volume. Diesel fuel was injected intermittently into the atmosphere using a 5-hole injector nozzle. The diameter of the nozzle orifice was 0.113 mm. The injection pressure was set at 80 and 120 MPa by using a common rail system and the ambient pressure was varied from 0.1 to 3 MPa. The period of injector solenoid energizing was set at 3.0 ms. Droplets were evaluated in a period of 0.2 ms just after the spray tip passed the measurement position. Measurement positions were located at 6, 9 and 12 mm from the nozzle exit. The effect of ambient pressure on the droplet velocity in the near-nozzle region was unremarkable.

A 2-D phase doppler technique was used for the measurements of the velocity, size, and flight direction of droplets in diesel sprays. The data acquisition rate of the phase doppler system was 250 kHz. Diesel fuel sprays injected intermittently into the atmosphere were investigated. The injector orifice was 0.113 mm in diameter. The rail pressure was set at 40 MPa by using a common rail system. The injection period was 3.0 ms and the time interval between injections was 330 ms. Measurement position was located at 40 mm from the nozzle exit for free sprays. In order to evaluate velocity vectors of each droplet, velocity components with angles plus and minus 45 degrees to the spray axis were measured. The data measured at each position was 10,000 and was accumulated over about 1,000 injections. It was found that most droplets near the spray center had velocity vectors along the spray axis.

A laser 2–focus velocimeter (L2F) has been applied for the measurements of velocity and size of droplets in the core region of diesel spray. The L2F had a micro–scale probe which consists of two foci. The distance between two foci was 14 µm and the focus size was nominally 3 µm. Valid data were extracted by the criteria that a downstream signal was sequentially observed after an upstream signal. The maximum data sampling rate of the L2F was set at 15 MHz. Fuel was intermittently injected into the atmosphere by using a common rail injector. The nozzle orifice diameter of the injector was 0.113 mm and the injection pressure was set at 70 MPa. Five measurement positions were located in the plane of 15 mm from the nozzle orifice. The L2F could detect droplets just after the spray tip reached the measurement position. Measurement result showed that the velocity and size of droplets in the spray core decreased at the off–axis region.

In order to clarify ignition characteristics of a HCCI engine, methanol and natural-gas were burnt in a single cylinder diesel engine fuelling with DME as an ignition source. The effect of fuel cetane number on low temperature reaction(LTR), high temperature reaction (HTR), knock limit temperature and misfire limit were compared between methanol and natural gas. It is found that ignition temperatures of LTR and HTR is dependent only on cetane number of the fuel, however, the maximum heat release rate of LTR is dependent not only on cetane number but also the fuel composition.

An advanced laser 2-focus velocimeter (L2F) has been applied to the measurement of droplet velocities and sizes in a dense region of diesel fuel spray. The maximum rate of data sampling of the L2F was set at 15 MHz. The fuel was injected into the atmosphere by using a common rail injector. The rail pressure was set at 40 and 70 MPa. The nozzle hole diameter of the injector was 0.113 mm. The L2F can detect droplets just after the spray tip reaches the measurement position 30 mm downstream from the nozzle. The result of the measurement shows that the higher injection pressure leads the higher droplet velocity in the core of the spray. It is clearly shown that the smaller droplets after active disintegration are dispersed spatially under higher injection pressure.

A laser 2-focus velocimeter (L2F) has been applied for the measurements of velocity and size of droplets in the core region of diesel spray. The L2F had a micro-scale probe which consists of two foci. The distance between two foci was 14 μm and the focus size was nominally 3 μm. Valid data were extracted by the criteria that a downstream signal was sequentially observed after an upstream signal. The maximum data sampling rate of the L2F was set at 15 MHz. Fuel was intermittently injected into the atmosphere by using a common rail injector. The nozzle orifice diameter of the injector was 0.113 mm and the injection pressure was set at 70 MPa. Five measurement positions were located in the plane of 15 mm from the nozzle orifice. The L2F could detect droplets just after the spray tip reached the measurement position. Measurement result showed that the velocity and size of droplets in the spray core decreased at the off-axis region.

In order to get fundamental information about the droplet disintegration in the core region of diesel fuel spray, an advanced laser 2-focus velocimeter (L2F) was used for the measurements of velocity and size of droplets. The L2F with micro-scale probe has high optical SN ratio and high spatial resolution. Measured was the fuel spray injected into the atmosphere intermittently from a single hole nozzle. The diameter of the orifice was 0.2 mm. Measurements were conducted on four planes where the axial distances were 10, 20, 30, and 40 mm respectively downstream from the orifice exit. As the injection pressure and needle valve lift change unsteadily in case of the intermittent injection spray, time change of spatial distributions of velocity and size was measured and time change of the joint probability density associated with velocity and size was examined.

Homogeneously charged natural gas was burned in a diesel engine assisted by a small amount of gas oil injection. The effects of the equivalence ratio of natural gas, the intake temperature and the EGR rate on ignition of gas oil, the burning rate of natural gas and the knock limit were clarified experimentally. As results, a marked improvement in the trade-off between smoke and NOx was obtained maintaining a high thermal efficiency by a combination between the natural gas charge rate, the EGR rate, the intake preheating and the nozzle orifice size suitable at each engine load.

The effect of port water injection on NOx formation was examined theoretically as well as experimentally. In the experiment, water was injected into each suction port of a four cylinder turbocharged DI diesel engine using gasoline injectors. The exhaust NOx was reduced significantly by port water injection, and about 50 % reduction in NOx concentration was attained under various engine operation conditions by injecting the amount of water of 0.03 kg per unit kg of dry air. Comparing the experimental results and the analytical ones based on the two-zone model developed by the authors, it is shown that the NOx reduction rate due to port water injection is dependent on the equivalent absolute humidity of the injected water and is independent on engine load, fuel injection timing and water injection timing.

For reducing the exhaust emissions and improving the ignition characteristics, the effect of pilot injection was investigated experimentally in a turbocharged direct injection diesel engine. The pilot injection quantity was varied by changing the seat diameter of the Dodge plunger installed in the newly developed pilot injector while the separation period between the beginning of pilot injection and that of main injection was fixed at a short interval in the present experiment. The pilot injection effect on combustion was compared with the case of normal injection in two fuel oils with the cetane indexes of 55 and 40 respectively.

Cylinder pressures at several locations and the radiant heat emission were measured simultaneously in order to better understand the combustion behavior in the combustion chamber of a high speed DI diesel engine. The radiant measurements utilized an optical fiber thermometer (OFT) with a light pipe sensor. The exhaust emissions of NOx, smoke and particulates were also measured. The formation of NOx and soot and the soot burn-up processes were analyzed applying an in-cylinder two-zone model. The results were compared with the experiment. It was confirmed that diffusion burning stage started close to the first peak of the heat release rate curve. The OFT output was closely related to the diffusion combustion process. The measured exhaust smoke correlated well with the cumulative diffusion combustion quantity. The dry soot in the particulate emission also correlated well with the Bosch smoke density except for the cases of high sulfur fuel and water-emulsified fuel.

A new method named the modified correlation method with slotting (MCS) has been proposed to analyze the turbulence scale accurately from the random discrete data with non-uniform time intervals, usually obtained by LDV measurements. The reliability of the method was confirmed by the model data. By applying the method, the authors have analyzed the air flow and the turbulence in a combustion chamber of a motored diesel engine under the conditions of three different intensities of suction swirl and also around the fuel spray injected intermittently under atmospheric condition. The main feature of turbulence confirmed were as follows. The integral time scale increased once at the beginning of the compression stroke and then decreased toward the compression top dead center.