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Technical Paper

An Experimental Study of the Spray Characteristics of Pressure-Swirl Atomizers for DISI Combustion Systems

This paper presents results from a comprehensive experimental study of high-pressure pressure-swirl gasoline injectors tested under a range of simulated operating conditions. This study encompassed photographic analysis of single spray sequences and simultaneous measurement of axial velocity, radial velocity and diameter at point locations using the phase-doppler technique. The combination of these measurement techniques permitted an insight into the fluid dynamics of the injected spray and its development with time. Five primary stages in the spray-history were identified and numerated with experimental data.
Technical Paper

Effects of Fuel Composition on Mixture Formation in a Firing Direct-Injection Spark-Ignition (DISI) Engine: An Experimental Study using Mie-Scattering and Planar Laser-Induced Fluorescence (PLIF) Techniques

Two-dimensional Mie-scattering and laser-induced fluorescence techniques were applied to investigate the effects of fuel composition on mixture formation within a firing direct-injection spark-ignition (DISI) engine. A comparison was made between the spray characteristics and in-cylinder fuel distributions resulting from the use of a typical multi-component gasoline (European specification premium-grade unleaded), a single-component research fuel (iso-octane), and a three-component research fuel (iso-pentane, iso-octane and n-nonane). Studies were performed at three different injection timings under cold and part-warm conditions. The results indicate that fuel composition affects both the initial spray formation and the subsequent mixture formation process. Furthermore, the sensitivity of the mixing process to the effects of fuel volatility was shown to depend on injection timing.
Technical Paper

Effects of Fuel Injection Pressure in an Optically-Accessed DISI Engine with Side-Mounted Fuel Injector

This paper presents the results of an experimental study into the effects of fuel injection pressure on mixture formation within an optically accessed direct-injection spark-ignition (DISI) engine. Comparison is made between the spray characteristics and in-cylinder fuel distributions due to supply rail pressures of 50 bar and 100 bar subject to part-warm, part-load homogeneous charge operating conditions. A constant fuel mass, corresponding to stoichiometric tune, was maintained for both supply pressures. The injected sprays and their subsequent liquid-phase fuel distributions were visualized using the 2-D laser Mie-scattering technique. The experimental injector (nominally a hollow-cone pressure-swirl design) was seen to produce a dense filled spray structure for both injection pressures under investigation. In both cases, the leading edge velocities of the main spray suggest the direct impingement of liquid fuel on the cylinder walls.
Technical Paper

Effects of Injection Timing on Liquid-Phase Fuel Distributions in a Centrally-Injected Four-Valve Direct-Injection Spark-Ignition Engine

An experimental study was carried out to investigate the effects of fuel injection timing on the spatial and temporal development of injected fuel sprays within a firing direct-injection spark-ignition (DISI) engine. It was found that the structure of the injected fuel sprays varied significantly with the timing of the injection event. During the induction stroke and the early part of the compression stroke, the development of the injected fuel sprays was shown to be controlled by the state of the intake and intake-generated gas flows at the start of injection (SOI).The relative influence of these two flow regimes on the injected fuel sprays during this period was also observed to change with injection timing, directly affecting tip penetration, spray/wall impingement and air-fuel mixing. Later in the compression stroke, the results show the development of the injected fuel sprays to be dominated by the increased cylinder pressure at SOI.
Technical Paper

Fiber Optic Sensor for Crank Angle Resolved Measurements of Burned Gas Residual Fraction in the Cylinder of an SI Engine

A fiber optic infrared spectroscopic sensor was developed to measure the crank angle resolved residual fraction of burned gas retained in the cylinder of a four-stroke SI engine. The sensor detected the attenuation of infrared radiation in the 4.3 μm infrared vibrational-rotational absorption band of CO2. The residual fraction remaining in the cylinder is proportional to the CO2 concentration. The sensor was tested in a single-cylinder CFR spark ignition engine fired on propane at a speed of 700 rpm. The sensor was located in one of two spark plug holes of the CFR engine. A pressure-transducer-type spark plug was used to record the cylinder pressure and initiate the spark. The temporal resolution of the measurements was 540 μs (equivalent to 2.3 crank angle degrees) and the spatial resolution was 6 mm. Measurements were made during the intake and compression stroke for several intake manifold pressures. The compression ratio of the engine was varied from 6.3 to 9.5.
Technical Paper

Further Experiments on the Effects of In-Cylinder Wall Wetting on HC Emissions from Direct Injection Gasoline Engines

A recently developed in-cylinder fuel injection probe was used to deposit a small amount of liquid fuel on various surfaces within the combustion chamber of a 4-valve engine that was operating predominately on liquefied petroleum gas (LPG). A fast flame ionization detector (FFID) was used to examine the engine-out emissions of unburned and partially-burned hydrocarbons (HCs). Injector shut-off was used to examine the rate of liquid fuel evaporation. The purpose of these experiments was to provide insights into the HC formation mechanism due to in-cylinder wall wetting. The variables investigated were the effects of engine operating conditions, coolant temperature, in-cylinder wetting location, and the amount of liquid wall wetting. The results of the steady state tests show that in-cylinder wall wetting is an important source of HC emissions both at idle and at a part load, cruise-type condition. The effects of wetting location present the same trend for idle and part load conditions.