Search Results

Fuel-air mixing in a direct-injection SI engine was studied to further improve full-load torque output. The fuel-injection location of DI vs. PFI results in different heat sources for fuel evaporation, hence a DI engine has been found to exhibit higher volumetric efficiency and lower knocking tendency, resulting in higher full-load torque output [1]. The ability to change injection timing of the DI engine affects heat transfer and mixture temperature, hence later injection results in lower knocking tendency. Both the higher volumetric efficiency and the lower knocking tendency can improve engine torque output. Improving volumetric efficiency requires that the fuel is injected during the intake stroke. Reducing knocking tendency, in contrast, requires that the fuel is injected late during the compression stroke. Thus, a strategy of split injection was proposed to compromise the two competing requirements and further increase direct-injection SI engine torque output.

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.

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.

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.

The fiber optic spark plug was used in conjunction with a piezoelectric pressure transducer to collect combustion diagnostic data on four production engines designed to generate quiescent, swirl, and tumble charge motions. Spark advance was varied under low speed, low load conditions to investigate changes in flame kernel behavior and in-cylinder charge motion as functions of crank angle and spark advance. Two flame kernel models were filled to the data and a critical comparison of the models was conducted. Flame kernel behavior was represented by three values: convection velocity, growth rate, and convection direction. Convection velocity was highest in the swirl chambers. It also varied considerably among cylinders in the same engine. Growth rate correlated well with 0-2% burn but showed negligible correlations with later burn or IMEP. Convection direction proved useful in determining flow direction near the plug.

Current demands for high fuel efficiency and low emissions in automotive powerplants have drawn attention to the two-stroke engine configuration. The present study measured trapping and scavenging efficiencies of a firing two-stroke spark-ignition engine by in-cylinder gas composition analysis. Intermediate results of the procedure included the trapped air-fuel ratio and residual exhaust gas fraction. Samples, acquired with a fast-acting electromagnetic valve installed in the cylinder head, were taken of the unburned mixture without fuel injection and of the burned gases prior to exhaust port opening, at engine speeds of 1000 to 3000 rpm and at 10 to 100% of full load. A semi-empirical, zero-dimensional scavenging model was developed based on modification of the non-isothermal, perfect-mixing model. Comparison to the experimental data shows good agreement.

For several years, a single-cylinder, spark-ignited engine without catalyst has been operated at Ford on single-component fuels that are constituents of gasoline as well as on simple fuel mixtures. This paper presents a review of these experiments as well as others pertinent to understanding hydrocarbon emissions. The engine was run at four steady-state conditions which are typical of normal operation. The fuel structure and the engine operating conditions affected both the total HC emissions and the reactivity of these emissions for forming photochemical smog in the atmosphere. These experiments identified major precursor species of the toxic HC emissions benzene and 1,3-butadiene to be alkylated benzenes and either straight chain terminal olefins or cyclic alkanes, respectively. In new data presented, the primary exhaust hydrocarbon species from MTBE combustion is identified as isobutene.

Multidimensional modeling is used to study air-fuel mixing in a direct-injection spark-ignition engine. Emphasis is placed on the effects of the start of fuel injection on gas/spray interactions, wall wetting, fuel vaporization rate and air-fuel ratio distributions in this paper. It was found that the in-cylinder gas/spray interactions vary with fuel injection timing which directly impacts spray characteristics such as tip penetration and spray/wall impingement and air-fuel mixing. It was also found that, compared with a non-spray case, the mixture temperature at the end of the compression stroke decreases substantially in spray cases due to in-cylinder fuel vaporization. The computed trapped-mass and total heat-gain from the cylinder walls during the induction and compression processes were also shown to be increased in spray cases.

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.

A small-bore 4-stroke single-cylinder stratified-charge DISI engine using an air-forced fuel injection system has been designed and tested under various operating conditions. At light loads, fuel consumption was improved by 16∼19% during lean, stratified-charge operation at an air-fuel ratio of 37. NOx emissions, however, were tripled. Using EGR during lean, stratified-charge operation significantly reduced NOx emissions while fuel consumption was as low as the best case without EGR. It was also found that combustion and emissions near the lean limit were a strong function of the combination of injection and spark timings, which affect the mixing process. Injection pressure, air injection duration, and time delay between fuel and air injections also played a role. Generating in-cylinder air swirl motion slightly improved fuel economy.

The effects of fuel injection and spark timing on engine-out, regulated (total HC, NOx, and CO) and speciated HC emissions have been investigated for a 0.31L, single-cylinder, direct-injection, spark-ignition (DISI) engine equipped with an air-forced fuel injector. When the timing of the start of the air injection (SOA) is varied during high stratification operation, the mole fractions of all regulated emissions vary sharply over relatively small (20-30 crank angle degrees) changes in SOA. In addition, the distribution of exhaust hydrocarbon species changes significantly. As stratification increases, the contribution of unburned paraffinic fuel components to the HC emissions decreases by a factor of two while the olefinic partial oxidation products increase. When the spark timing is varied during high stratification operation, the HC emissions increase sharply as the spark timing is retarded relative to MBT.

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.