Steven Wooldridge

Measurement and Analysis of the Residual Gas Fraction in an SI Engine with Variable Cam Timing

A spontaneous Raman scattering diagnostic was used to measure the residual fraction in a single-cylinder, 4-valve optically accessible engine. The engine was operated at 1500 rpm on pre-vaporized iso-octane at several intake manifold pressures (50-90 kPa). Cam phasing was varied to determine the effect of intake valve timing and valve overlap on the residual mass fraction of the engine. A simple model based on the ideal Otto cycle and 1D gas flow through the exhaust valves was proposed to analyze the results of the Raman experiment. The model showed good agreement (R 2 =0.91) with the experimental results and demonstrated its potential for use as a method to estimate the residual fraction in an engine from available dynamometer data. The experimental results showed that the residual fraction was reduced at higher manifold pressures due to less backflow through the exhaust valves and varied with intake cam phasing. The variation with intake cam phasing was determined by the gas properties in the cylinder when the intake valve opened. When the engine was stable (Coefficient of Variance (CoV) imep < 3%), changing the manifold pressure did not affect the portion of the residual fraction due to mass trapped at intake valve opening (IVO) and influenced the residual levels by reducing the residual level due to backflow.

An Imaging Study of Compression Ignition Phenomena of Iso-Octane, Indolene, and Gasoline Fuels in a Single-Cylinder Research Engine

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from 0.69 to 0.27. The time-resolved imaging and pressure data show that high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data. DOI: 10.1115/1.2898720

Applications of CFD Modeling in GDI Engine Piston Optimization

This paper describes a CFD modeling based approach to address design challenges in GDI (gasoline direct injection) engine combustion system development. A Ford in-house developed CFD code MESIM (Multidimensional Engine Simulation) was applied to the study. Gasoline fuel is multi-component in nature and behaves very differently from the single component fuel representation under various operating conditions. A multi-component fuel model has been developed and is incorporated in MESIM code. To apply the model in engine simulations, a multi-component fuel recipe that represents the vaporization characteristics of gasoline is also developed using a numerical model that simulates the ASTM D86 fuel distillation experimental procedure. The effect of the multi-component model on the fuel air mixture preparations under different engine conditions is investigated. The modeling approach is applied to guide the GDI engine piston designs. Effects of piston designs on the fuel air mixture preparation are presented. It is found that the multi-component fuel model is critical to the accuracy of the model prediction of the fuel air preparation process, particularly under cold start conditions.

A multi-axis imaging study of spark-assisted homogeneous charge compression ignition phenomena in a single-cylinder research engine

High-speed imaging combined with the optical access provided by a single-cylinder research engine offer the ability to directly study ignition and combustion phenomena. Such data provide valuable insight into the physical and chemical mechanisms important in advanced engine combustion strategies. In this study, crank-angle resolved chemiluminescence imaging data both orthogonal to and along the piston axis were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using indolene. This preliminary study focused on identifying how multi-axis imaging can contribute to understanding the effects of spark-assist on HCCI performance. Operating conditions of advanced spark ignition timing for extending the lean limits of bulk charge compression ignition were used. The experiments were performed at a fixed equivalence ratio of φ = 0.56, with fixed intake conditions (wide open throttle with air preheat). The multi-axis imaging provides a clear indication of the propagation of a reaction front from the spark kernel. The combination of orthogonal and axial views may provide valuable information spatially resolving volumetric heat release, thereby providing an indication of the fractional energy release due to the spark assist compared to the energy released by auto-ignition.Copyright

Stratified-charge fuel preparation influence on the misfire rate of a DISI engine

The influence of mixture preparation on misfires at idle in a Direct Injection Spark Ignition (DISI) engine was investigated. A wall-guided DISI engine was run at idle conditions in a stratified charge mode (750 rpm / 90 kPa MAP). Images of the mixture composition at the spark plug were taken at spark timing using Planar Laser Induced Fluorescence (PLIF.) for several different End-of-injection (EOI) timings and spark timings. Cylinder pressure data were acquired simultaneously with the images to identify misfire cycles. he misfire rate was found to increase as the EOI timing was advanced from the optimal timing, defined by maximum stability and lowest ISFC. Images show that the misfire rate at a particular operating condition can be correlated to the fuel distribution and the location of the stratified charge in the engine. Cycles that showed a lower amount of stratification (overmixing) and/or high gradients in fuel concentration near the spark plug were the least stable. At the most advanced EOI timings, the charge was shown to have overpenetrated and moved past the spark plug in its trajectory, increasing the misfire rate. Retarding the spark timing yielded the same result as advancing the EOI. Advancing the spark timing resulted in a charge that appeared to still be in the process of exiting the bowl during the spark event and increased the misfire rate. Individual misfire cycles were also compared to average firing cycles. These cycles displayed both a large amount of variation from the mean and very poor charge formation, in terms of location and fuel concentration.

Spray Development and Wall Impingement of Ethanol and Gasoline in an Optical Direct Injection Spark Ignition Engine

The effects of ethanol on spray development and wall impingement of a direct injection spark ignition (DISI) engine was investigated using high-speed imaging of the fuel spray in an optically-accessible engine. Neat anhydrous ethanol (E100), reference grade gasoline (E0) and a 50% blend (by volume) of gasoline and ethanol (E50) were used in the study. The experiments were conducted using continuous firing conditions for an intake manifold absolute pressure of 57 kPA, and engine speed of 1500 RPM. Retarded fuel injection timing was used (with start of injection at 250 °bTDC) to isolate the effects of cylinder wall impingement, and lean fuel-to-air ratios (ϕ=0.8–0.9) were used to minimize sooting and coating of the transparent cylinder liner. The effects of three engine coolant temperatures (25, 60 and 90 °C) and two fuel rail pressures (100 and 150 bar) on the features of the spray and the spray interaction with the wall were studied for the different fuels. Quantitative metrics were defined to analyze the spatial features of the spray related to wall impingement. Gasoline (E0) sprays exhibited higher sensitivity to coolant temperature compared to ethanol (E100) in terms of the shape of the spray and wall impingement. Higher fuel injection pressure increased the spray tip penetration rate and fuel impingement with the wall for E0 and E100, despite creating wider plume angles of the fuel sprays.Copyright

A Comparison of Imaging of Compression Ignition Phenomena of Iso-Octane, Indolene, and Gasoline Fuels in a Single-Cylinder Research Engine

High-speed imaging combined with the optical access provided by a research engine offer the ability to directly image and compare ignition and combustion phenomena of various fuels. Such data provide valuable insight into the physical and chemical mechanisms important in each system. In this study, crank-angle resolved imaging data were used to investigate homogeneous charge compression ignition (HCCI) operation of a single-cylinder four-valve optical engine fueled using gasoline, indolene, and iso-octane. Lean operating limits were the focus of the study with the primary objective of identifying different modes of reaction front initiation and propagation for each fuel. HCCI combustion was initiated and maintained over a range of lean conditions for various fuels, from φ = 0.77 to 0.27. The time-resolved imaging and pressure data show high rates of heat release in HCCI combustion correlate temporally to simultaneous, intense volumetric blue emission. Lower rates of heat release are characteristic of spatially-resolved blue emission. Gasoline supported leaner HCCI operation than indolene. Iso-octane showed a dramatic transition into misfire. Similar regions of preferential ignition were identified for each of the fuels considered using the imaging data.Copyright