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Transient behavior of the engine is one of the most crucial factors for motorcycle features. Characterization of the fuel film with port fuel injection (PFI) is necessary to enhance this feature with keeping others, such as high output, low emissions and good fuel consumption. In order to resolve the complicated phenomena in real engine condition into simple physical issues, a simulated intake port was used in our research with Laser Induced Fluorescence (LIF) technique to allow accurate measurement of the fuel film thickness, complemented by visualization of the film development and spray behavior using high-speed video imaging. Useful results have been conducted from the parametric studies with various sets of conditions, such as injection quantity, air velocity and port backpressure.

In a motorcycle gasoline engine, the port fuel injection system is rapidly spread. Compared to an automotive engine, the injected fuel does not impinge on the intake valve due to space restriction to install the injector. In addition, as the air flow inside the intake pipe may become very fast and has large cycle-to-cycle variation, it is not well found how the injector should be installed in the intake pipe to prepare “good” fuel-air mixture inside the intake pipe. In this study, the formation process of the fuel-air mixture is measured by using ILIDS system that is a 2-D droplets' size and velocity measurement system with high spatial resolution. Experiments with changing conditions such as flow speed and injection direction are carried out. As a result, the effects of injection direction, ambient flow speed and wall roughness on the fuel-air mixture formation process was examined, considering the three conditions of cold start, light to medium load operation and high load operation.

Measurements of flow, spray, combustion and performance characteristics are reported for a Hydra direct-injection diesel, based on the Ford 2.5 L, engine and equipped with a variable-swirl port, a unit fuel injector and optical access through the liner and piston. The results provide links between the pre-combustion and combustion flow and, at the same time, between purpose-built single-cylinder optical engines and multi-cylinder production engines of nearly identical combustion chamber geometry. In particular, the spray penetration was found to depend on engine speed, rather than load, with velocities up to around 260 m/s at atmospheric pressure and temperature which are reduced by a factor of 2.5 under operating conditions and seem to be unaffected by swirl. The duration of combustion was reduced with increasing swirl and ignition delay increased linearly with engine speed.

Local measurements of the mean and rms velocities have been obtained by laser Doppler velocimetry in the coolant passages of a transparent model of a Ford 2.5L diesel cylinder head and block at a steady flowrate of 6.83 × 10-4 M3/s. The simulation of the coolant fluid by a mixture of hydrocarbon fluids at a predetermined constant temperature allowed accurate matching of the refractive index to that of the acrylic model, thus providing optical access for LDV measurements of the internal flow in sensitive areas where cooling is essential to prevent metal-fatigue failure. The results were obtained in sufficient detail to allow further validation of CFD coolant flow models.

By using empirical and semi-empirical relationships previously reported in the literature, non-linear viscoelastic properties of a number of lubricants have been determined from their linear viscoelastic behaviour, as measured by an oscillatory rheometer. Similarly to polymeric viscosity index improved (VII) lubricants, non-polymeric mineral blends were also shown to display viscoelastic behaviour. A general equation is suggested that allows the first normal stress difference which characterises the viscoelastic behaviour of lubricants to be expressed as a function of the shear viscosity.

Direct flame imaging and pressure analysis were applied to the combustion of gasoline and compressed natural gas (CNG) in a single-cylinder, four-valve spark-ignition engine equipped with optical access via quartz windows in the cylinder liner and piston crown. Tests were performed at three engine speed/load conditions and at equivalence ratios of 1.0, 0.9 and 0.8. The four-valve head incorporated two different port geometries, with and without metal sleeves to deflect the intake air flow, in order to investigate the effect of tumble strength on combustion and engine-out emissions of unburned hydrocarbons and NOx. The results showed that sleeving of the intake ports produced a significant increase in IMEP and a reduction in CoV IMEP for both CNG and gasoline, due to the greatly reduced bum duration.

Laser Doppler velocimetry, phase Doppler anemometry and Mie scattering were applied to a single-cylinder, four-valve, spark-ignition gasoline research engine equipped with a fully transparent liner and piston, to obtain information about the tumble flow and the droplet size and velocity distributions during induction and compression, for lean air/fuel mixture ratios of 17.5 and 24 and with closed-valve and open-valve fuel injection. The mixture distribution obtained with the two injection strategies was correlated with flame images, pressure analysis and exhaust emissions which confirmed the advantages of combining open-valve injection with tumble to allow stable and efficient engine operation at an air/fuel ratio of 24 through charge stratification and faster flame growth.

The ability of certain induction systems to enhance turbulence levels at the time of ignition, through formation of long-lived tumbling vortices on the plane of the valve and cylinder axes, has been investigated in a two-valve spark-ignition engine by rotating the intake port at 90° and 45° to the orientation of production directed ports. Detailed measurements of the three velocity components, obtained by laser velocimetry, revealed that the 90° port generated a pure tumble motion, with a maximum tumbling vortex ratio of 1.5 at 295°CA, zero swirl, and 42% turbulence enhancement relative to the standard configuration, while the 45° port gave rise to a combined tumble/swirl structure with a maximum tumbling vortex ratio of 0.5 at 285°CA, swirl ratio of 1.0 at TDC, and turbulence enhancement of 24%. The implications of the two types of flow structures for combustion are discussed.

The spatial and temporal characteristics of a diesel spray injected into the atmosphere through a multi-hole nozzle used in small DI Diesel engines have been investigated by laser techniques as a function of pump speed and load. The results showed that spray tip penetration and velocity depend on injection frequency rather than injected volume and the spray is asymmetric during the early and main part of the injection period. In the time/space domain different structures have been identified within the injection period, with the early injection period characterized by a well atomized cloud of droplets, the main period by the spray head and a dense core and the late injection period by the disintegrating dense core and the spray tail. IN DIRECT-INJECTION DIESEL ENGINES for passenger cars, fuel is injected through multi-hole nozzles at high pressure to promote mixing with the rapidly swirling air inside the combustion chamber.

Gasoline fueled Homogeneous Charge Compression Ignition (HCCI) combustion with internal exhaust gas re-circulation using Negative Valve Overlap (NOL) was investigated by means of calculation and experiment in order to apply this technology to practical use with sufficient operating range and with acceptable emission and fuel consumption. In this paper we discuss the basic characteristics of NOL-HCCI with emphasis on the influence of intake valve timing on load range, residual gas fraction and induction air flow rate. Emission and fuel consumption under various operation conditions are also discussed. A water-cooled 250cc single cylinder engine with a direct injection system was used for this study. Three sets of valve timing were selected to investigate the effect of intake valve opening duration. Experimental results demonstrated that an engine speed of approximately 2000rpm yields an NMEP (Net Mean Effective Pressure) range from 200kPa to 400kPa.

The predictive capability of Lagrangian and Eulerian multi-dimensional computational fluid dynamics models accounting for the onset and development of cavitation inside Diesel nozzle holes is assessed against experimental data. These include cavitation images available from a real-size six-hole mini-sac nozzle incorporating a transparent window as well as high-speed/CCD images and LDV measurements of the liquid velocity inside an identical large-scale fully transparent nozzle replica. Results are available for different cavitation numbers, which correspond to different cavitation regimes forming inside the injection hole. Discharge coefficient measurements for various real-size nozzles operating under realistic injection pressures are also compared and match well with models' predictions.

This computational study compares predictions and experimental results for the use of direct injected iso-octane fuel during the negative valve overlap (NVO) period to achieve HCCI combustion. The total fuel injection was altered in two ways. First the pre-DI percent, (the ratio of direct injected fuel during the NVO period “pre-DI” to the secondary fuel supplied at the intake manifold “PI”), was varied at a fixed pre-DI injection timing, Secondly the timing of the pre-DI injection was varied while all of the fuel was supplied during the NVO period. A multi-zone, two-dimensional CFD simulation with chemistry was performed using KIVA-3V release 2 implemented with the CHEMKIN solver. The simulations were performed during the NVO period only.

A single cylinder Yamaha research engine was operated with gasoline HCCI combustion using negative valve overlap (NVO). The injection strategy for this study involved using fuel injected directly into the cylinder during the NVO period (pre-DI) along with a secondary injection either in the intake port (PI) or directly into the cylinder (DI). The effects of timing of the pre-DI injection along with the percent of fuel injected during the pre-DI injection were studied in two sets of experiments using secondary PI and DI injections in separate experiments. Results have shown that by varying the pre-DI timing and pre-DI percent the main HCCI combustion timing can be influenced as a result of varied heat release during the negative valve overlap period along with hypothesized varied degrees of reformation of the pre-DI injected fuel. In addition to varying the main combustion timing the ISFC, emissions and combustion stability are all influenced by changes in pre-DI timing and percent.

The performance of multi-hole injectors designed for use in second-generation direct-injection gasoline engines has been characterised in a constant-volume chamber. Two types of multi-hole injector have been used: the first has 11 holes, with one hole on the axis of the injector and the rest around the axis at 30 degrees apart, and the second has 6 asymmetric holes located around the nozzle axis. Measurements of droplet axial and radial velocity components and their diameter were obtained using a 2-D phase Doppler anemometer (PDA) at injection pressures up to 120 bar, chamber pressures from atmospheric to 8 bar, and ambient temperatures. Complementary spray visualisation made use of a pulsed light and a CCD camera synchronised with the injection process.

A transparent enlarged model of a six-hole injector used in the development of emerging gasoline direct-injection engines was manufactured with full optical access. The working fluid was water circulating through the injector nozzle under steady-state flow conditions at different flow rates, pressures and needle positions. Simultaneous matching of the Reynolds and cavitation numbers has allowed direct comparison between the cavitation regimes present in real-size and enlarged nozzles. The experimental results from the model injector, as part of a research programme into second-generation direct-injection spark-ignition engines, are presented and discussed. The main objective of this investigation was to characterise the cavitation process in the sac volume and nozzle holes under different operating conditions. This has been achieved by visualizing the nozzle cavitation structures in two planes simultaneously using two synchronised high-speed cameras.

The near nozzle exit flow and spray structure generated by an enlarged model of a second generation pintle type outwards opening injector have been investigated under steady flow conditions as a function of flow-rate and needle lift. A high resolution CCD camera and high-speed video camera have been employed in this study to obtain high-magnification images of the internal nozzle exit flow in order to identify the origin of string ligaments/droplets formation at the nozzle exit. The images of the flow around the nozzle seat area showed clearly that air was entrained from outside into the nozzle seat area under certain flow operating conditions (low cavitation number, CN); the formed air pockets inside the annular nozzle proved to be the main cause of the breaking of the fuel liquid film into strings as it emerged from the nozzle with a structure consisting of alternating thin and thick liquid filaments.

A laser-induced fluorescence (LIF) system has been developed to obtain measurements of the instantaneous lubricant film thickness in the piston-cylinder assembly of a firing single-cylinder, direct-injection diesel engine. Measurements were made at top-dead-centre (TDC), mid-stroke and bottom-dead-centre (BDC) position by means of three fibre optic probes inserted into the cylinder liner and mounted flush with its surface. Following extensive repeatability tests, the cycle-averaged lubricant film thickness was estimated for different multi-grade oils as a function of engine speed, load and temperature. The results quantified the dependence of the film thickness ahead, under and behind the piston rings on oil chemistry and viscometric properties, thus confirming the important role of the LIF technique in the development and formulation of new engine oils.

Laser induced fluorescence (LIF) was used in the cylinder liner of a firing single-cylinder direct-injection diesel engine to characterise the development of the lubricant film during the first 200 engine cycles under cold-start conditions. The results have provided information on the rate of oil film development which has proved to be a highly unsteady process due to the complicated oil transport processes through the ring-pack.

Multi-dimensional computational efforts using comprehensive and skeletal kinetics have been made to investigate the cool flame region in HCCI combustion. The work was done in parallel to an experimental study that showed the impact of the negative temperature coefficient and the cool flame on the start of combustion using different fuels, which is now the focus of the simulation work. Experiments in a single cylinder CFR research engine with n-butane and a primary reference fuel with an octane number of 70 (PRF 70) were modeled. A comparison of the pressure and heat release traces of the experimental and computational results shows the difficulties in predicting the heat release in the cool flame region. The behavior of the driving radicals for two-stage ignition is studied and is compared to the behavior for a single-ignition from the literature. Model results show that PRF 70 exhibits more pronounced cool flame heat release than n-butane.

A single cylinder CFR research engine has been run in HCCI combustion mode at the rich and the lean limits of the homogeneous charge operating range. To achieve a variation of the degree of charge stratification, two GDI injectors were installed: one was used for generating a homogeneous mixture in the intake system, and the other was mounted directly into the side of the combustion chamber. At the lean limit of the operating range, stratification showed a tremendous improvement in IMEP and emissions. At the rich limit, however, the stratification was limited by the high-pressure rise rate and high CO and NOx emissions. In this experiment the location of the DI injector was in such a position that the operating range that could be investigated was limited due to liquid fuel impingement onto the piston and liner.