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A quasidimensional engine simulation which uses the concepts of fractal geometry to model the effects of turbulence on flame propagation in a homogeneous charge SI engine has been developed. Heat transfer and blowby/crevice flow submodels are included in this code and the submodels chosen are found to be reasonable. The model predictions of cylinder pressure histories are then compared with experimental data over a range of loads, equivalence ratios, and engine speeds. The model is not adjusted in any manner to yield better agreement with the data, other than by tuning the simple turbulence model used so as to yield agreement with data for the nonreacting flow. However, current information about the flame wrinkling scales in an engine is inadequate. Therefore, predictions are made for three different assumptions about the flame wrinkling scales which span the range of physically possible scales.

A quasi-dimensional model for a direct injection diesel engine was developed based on experiments at Sandia National Laboratory. The Sandia researchers obtained images describing diesel spray evolution, spray mixing, premixed combustion, mixing controlled combustion, soot formation, and NOx formation. Dec [1] combined all of the available images to develop a conceptual diesel combustion model to describe diesel combustion from the start of injection up to the quasi-steady form of the jet. The end of injection behavior was left undescribed in this conceptual model because no clear image was available due to the chaotic behavior of diesel combustion. A conceptual end-of-injection diesel combustion behavior model was developed to capture diesel combustion throughout its life span. The compression, expansion, and gas exchange stages are modeled via zero-dimensional single zone calculations.

It is a very challenging problem to reliably ignite extremely lean mixtures, especially for the low speed, high load conditions of large-bore natural gas engines. If these engines are to be use for the distributed power generation market, it will require operation with higher boost pressures and even leaner mixtures. Both place greater demands on the ignition system. The railplug is a very promising ignition system for lean burn natural gas engines with its high-energy deposition and high velocity plasma arc. It requires care to properly design railplugs for this new application, however. For these engines, in-cylinder pressure and mixture temperature are very high at the time of ignition due to the high boost pressure. Hot spots may exist on the electrodes of the ignitor, causing pre-ignition problems. A heat transfer model is proposed in this paper to aid the railplug design. The electrode temperature was measured in an operating natural gas engine.

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.

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.

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 effects of fuel properties on the emissions of a production vehicle with a gasoline direct injection engine operating over the Federal Test Procedure (FTP) cycle were investigated. The vehicle used was a 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine. Engine-out and tailpipe FTP emissions for six fuels and a California Phase 2 RFG reference fuel are presented. Four of the test fuels were blended from refinery components to meet specified distillation profiles. The remaining test fuels were iso-octane and toluene, an iso-alkane and an aromatic with essentially the same boiling point (at atmospheric pressure) that is near the T50 point for the blended fuels. Statistically significant effects, at the 95% confidence level, of the fuels on tailpipe emissions were found. Correlations were sought between the properties of the five blends and the Emissions Indices for engine-out hydrocarbons and NOx and for tailpipe particulates.

Piston wetting can be isolated from the other sources of HC emissions from DISI engines by operating the engine predominantly on a gaseous fuel and using an injector probe to impact a small amount of liquid fuel on the piston top. This results in a marked increase in HC emissions. In a previous study, we used a variety of pure liquid hydrocarbon fuels to examine the influence of fuel volatility and structure on the HC emissions due to piston wetting. It was shown that the HC emissions correspond to the Leidenfrost effect: fuels with very low boiling points yield high HCs and those with a boiling point near or above the piston temperature produce much lower HCs. All of these prior tests of fuel effects were performed at a single operating condition: the Ford World Wide Mapping Point (WWMP). In the present study, the effects of load and engine speed are examined.

A fiber optic instrumented spark plug was used to make time-resolved measurements of the fuel vapor concentration history near the spark gap in a four-valve DISI engine. Four different bulk flow were investigated. Several early and late injection timings were examined. The fuel concentration at the spark gap was correlated with IMEP. Emissions of CO, HCs, and NOx were related to the type of bulk flow. For both early and late injection the CoVs of fuel concentration were generally lowest for the weakest bulk flow which resulted in a stable stratification. Strong bulk flows convected the inhomogeneities through the measurement area near the spark plug resulting in both large intracycle and cycle-to-cycle variation in equivalence ratio at the time of ignition.

We have examined the influence of piston wetting on the size distribution and mass of particulate matter (PM) emissions in a SI engine using several different fuels. Piston wetting was isolated as a source of PM emissions by injecting known amounts of liquid fuel onto the piston top using an injector probe. The engine was run predominantly on propane with approximately 10% of the fuel injected as liquid onto the piston. The liquid fuels were chosen to examine the effects of fuel volatility and molecular structure on the PM emissions. A nephelometer was used to characterize the PM emissions. Mass measurements from the nephelometer were compared with gravimetric filter measurements, and particulate size measurements were compared with scanning electron microscope (SEM) photos of particulates captured on filters. The engine was run at 1500 rpm at the Ford world-wide mapping point with an overall equivalence ratio of 0.9.

The results of continuing investigations of a new type of ignitor, the railplugs are reported. Previous studies have shown that railplugs can produce a high velocity jet of plasma. Additionally, railplugs have the potential of assuring ignition under adverse conditions, such as for very dilute mixtures, because the railplug plasma is both hotter and has a larger mass than the plasma generated by a spark plug. In this paper, engine data are presented to demonstrate the improved dilution tolerance obtainable with railplugs. Data acquired using a railplug are compared to results obtained using a conventional spark plug and a spark plug with a wide spark gap, both using an inductive ignition system. The present results affirm earlier, preliminary findings that railplugs can extend the dilution limit and produce faster combustion.

An electronic particulate matter sensor (EPMS) developed at the University of Texas was used to characterize exhaust gases from a single-cylinder diesel engine and a light-duty diesel vehicle. Measurements were made during transient tip-in events with multiple sensor configurations in the single-cylinder engine. The sensor was operated in two modes: one with the electric field energized, and the other with no electric field present. In each mode, different characteristic signals were produced in response to a tip-in event, highlighting the two primary mechanisms of sensor operation. The sensor responded to both the natural charge of the particulate matter (PM) emitted from the engine, and was also found to create a signal by charging neutral particles. The characteristics of the two mechanisms of operation are discussed as well as their implications on the placement and operation of the sensor.

Cylinder liner rotation (Rotating Liner Engine, RLE) is a new concept for reducing piston assembly friction in the internal combustion engine. The purpose of the RLE is to reduce or eliminate the occurrence of boundary and mixed lubrication friction in the piston assembly (specifically, the rings and skirt). This paper reports the results of experiments to quantify the potential of the RLE. A 2.3 L GM Quad 4 SI engine was converted to single cylinder operation and modified for cylinder liner rotation. To allow examination of the effects of liner rotational speed, the rotating liner is driven by an electric motor. A torque cell in the motor output shaft is used to measure the torque required to rotate the liner. The hot motoring method was used to compare the friction loss between the baseline engine and the rotating liner engine. Additionally, hot motoring tear-down tests were used to measure the contribution of each engine component to the total friction torque.

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.

Researchers in the field of turbulent combustion have found fractal geometry to be a useful tool for describing and quantifying the nature of turbulent flames. This paper describes and compares several techniques for the fractal analysis of two dimensional (2-D) turbulent flame images. Four methods of fractal analysis were evaluated: the Area Method, the Box Method, the Caliper Method, and the Area-Caliper Method. These techniques were first applied to a computer-generated fractal image having a known fractal dimension and known cut-offs. It was found that a “window” effect can cause the outer cut-off to be underestimated. The Caliper Method was found to suffer from noise arising from the statistical nature of the analysis. The Area-Caliper Method was found to be superior to the other methods. The techniques were applied to two types of flame images obtained in a spark ignition engine: Mie scattering from particles seeded in the flow and laser induced fluorescence of OH.

Ignition of extremely lean or dilute mixtures is a very challenging problem. Therefore, it is essential for the engine development engineer to understand the fundamentals and limitations of existing ignition systems. This paper presents a new railplug ignition concept, a high-energy ignition system, which can enhance ignition of very lean mixtures by means of its high-energy deposition and high velocity jet of the plasma. This paper presents initial results of tests using an inductive ignition system, a capacitor discharge ignition system, and a railplug high-energy ignition system. Discharge characteristics, such as time-resolved voltage, current, and luminous emission were measured. Spark plug and railplug ignition are compared for their effects on combustion stability of a natural gas engine. The results show that railplugs have a very strong arc-phase that can ensure the ignition of very dilute mixtures.

The mixture preparation process was investigated in a direct-injected, 4-valve, SI engine under motored conditions. The interaction between the high-pressure fuel jet and the intake air-flow was observed. Laser-sheet droplet imaging was used to visualize the in-cylinder droplet distributions, and a single-component LDV system was used to measure in-cylinder velocities. The fuel spray was visualized with the engine motored at 1500 and 750 rpm, and with the engine stopped. It was observed that the shape of the fuel spray was distorted by the in-cylinder air motion generated by the intake air flow, and that this effect became more pronounced with increasing engine speed. Velocity measurements were made at five locations on the symmetry plane of the cylinder, with the engine motored at 750 rpm. Comparison of these measurements with, and without, injection revealed that the in-cylinder charge motion was significantly altered by the injection event.

The results of continuing investigations of a new type of ignitor, the railplug, are reported. Previous studies have shown that railplugs can produce a high velocity jet that is driven both by electromagnetic and thermal forces and that the jet velocity is strongly affected by the railplug geometry and by the electronics characteristics of the follow-on circuit. The present research was intended to provide insights about both: 1) how to match the electronics characteristics to a given geometry and 2) how the geometry affects the jet velocity. It is found that faster current rise times result in higher plasma velocities but current pulses that are too short result in rapid deceleration of the plasma while it is still within the railplug. It is also found that a fundamental geometric parameter is the ratio of the inductance gradient to the volume trapped within the railplug: the larger L′/V, the faster the resulting combustion process.

This paper presents the latest developments in the design and performance of an electronic particulate matter (PM) sensor developed at The University of Texas at Austin (UT) and suitable, with further development, for applications in active engine control of PM emissions. The sensor detects the carbonaceous mass component of PM in the exhaust and has a time-resolution less than 20 (ms), allowing PM levels to be quantified for engine transients. Sample measurements made with the sensor in the exhaust of a single-cylinder light duty diesel engine are presented for both steady-state and transient operations: a steady-state correlation with gravimetric filter measurements is presented, and the sensor response to rapid increases in PM emission during engine transients is shown for several different tip-in (momentary increases in fuel delivery) conditions.

The On-Board Distillation System (OBDS) extracts, from gasoline, a highly volatile crank fuel that enables simultaneous reduction of start-up fuel enrichment and significant ignition timing retard during cold-starting. In a previous paper we reported reductions in catalyst light-off time of >50% and THC emissions reductions >50% over Phase I of the FTP drive cycle. The research presented herein is a further development of the OBDS concept. For this work, OBDS was improved to yield higher-quality start-up fuel. The PCM calibration was changed as well, in order to improve the response to intake manifold pressure transients. The test vehicle was tested over the 3-phase FTP, with exhaust gases speciated to determine NMOG and exhaust toxics emissions. Also, the effectiveness of OBDS at generating a suitable starting fuel from a high driveability index test gasoline was evaluated.