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We present a multidimensional numerical model that calculates turbulent premixed flame propagation, assuming the flames have fractal geometries. Two scaling transformations, previously developed for laminar flames, are used to incorporate the fractal burning model in KIVA-II1, a numerical hydrodynamics code for chemically reactive flows. In this work the model is implemented for propane/air mixtures. For applications to internal combustion engines, we have also developed a fractal model for early flame kernel growth. Our multidimensional model can be used in experimental comparisons to test postulated fractal parameters, and we begin this task by comparing calculated results with measurements of propane/air combustion in a spark ignition engine. Good agreement is obtained between computed and measured flame positions and pressures in all cases except a low engine speed case.

Lean mixture combustion might be an important feature in the next generation of SI engines, while diluents (internal and external EGR) have already played a key role in the reductions of emissions and fuel consumption. Lean burn modeling is even more important for engine modeling tools which are sometimes used for new engine development. The effect of flame strain on flame speed is believed to be significant, especially under lean mixture conditions. Current quasi-dimensional engine models usually do not include flame strain effects and tend to predict burn rate which is too high under lean burn conditions. An attempt was made to model flame strain effects in quasi-dimensional SI engine models. The Ford model GESIM (stands for General Engine SIMulation) was used as the platform. A new strain rate model was developed with the Lewis number effect included.

In premixed turbulent combustion models, two mechanisms have been used to explain the increase in the flame speed due to the turbulence. The newer explanation considers the full range of turbulence scales which wrinkle the flame front so as to increase the flame front area and, thus, the flame propagation speed. The fractal combustion model is an example of this concept. The older mechanism assumes that turbulence enables the penetration of unburned mixtures across the flame front via entrainment into the burned mixture zone. The entrainment combustion or eddy burning model is an example of this mechanism. The results of experimental studies of combustion regimes and the flame structures in SI engines has confirmed that most combustion takes place at the wrinkled flame front with additional combustion taking place in the form of flame fingers or peninsulas.

Off-cycle emissions from seven different types of 1994 light-duty vehicles were examined The test fleet consisted of 19 individual vehicles including a passenger car, two makes of light light-duty trucks, and five types of heavy light-duty trucks The driving cycles used for these tests were the US06(hard acceleration, high speed) cycle and the 20 °F FTP (the “Cold FTP”) Conventional FTPs were done for comparison Each vehicle was usually operated on at least two of the following CNG, LPG, Federal Phase 1 reformulated gasoline (FP1 RFG), and a low sulfur certification gasoline For both the conventional FTP and the US06 cycles, the alternative fuels produce statistically significant benefits in Ozone Forming Potential and exhaust toxics but the NOx emissions are not statistically different from those when operating on FP1 RFG with at least 90% confidence During Cold FTP tests, the emissions of CO and of toxics when operating on FP1 RFG are not statistically different from those when operating on a low sulfur certification gasoline In contrast the alternative fuels produce statistically significant benefits in the emissions of both CO and toxics compared to either of the gasolines during Cold FTP tests The Reactivity Adjustment Factor calculated from the present conventional FTP results for CNG agrees closely with the CARB value However, the present RAF for LPG is about half CARB s value, which is believed to be a consequence of the low propene in Texas LPG compared to the high propene in California LPG The effects of the test type on the emissions are also discussed

The Texas Project is a multi-year study of the emissions and fuel economy of aftermarket conversions of light-duty vehicles, including passenger cars, light light-duty trucks, and heavy light-duty trucks. The test fleet, consisting of 86 mostly 1994 model year vehicles, includes eight different types of light-duty vehicles that have been converted to dual fueled operation for either CNG or LPG and corresponding gasoline controls. Virtually every type of aftermarket conversion technology (referred to as a “kit” for convenience) is represented in the test matrix: eight different CNG kits and seven different LPG kits, all of which have closed loop control systems. One goal of The Texas Project is to evaluate the different kits for each of the applications. One method used for evaluating the different kits was by assessing their potential for attaining LEV certification for each of the vehicle applications.

The Texas Project involves the conversion of light-duty vehicles, up to and heavy light-duty trucks, to bi-fueled vehicles using commercially available aftermarket CNG and LPG conversion systems. The test fleet includes 68 dual fueled conversions. Virtually every type of aftermarket conversion technology for CNG and LPG was evaluated: eight different CNG and seven different LPG conversion “kits”, all of which are modern systems incorporating closed-loop control. The kits were installed and calibrated according to the manufacturer's guidelines and recommendations. The emissions when operating on the alternative fuel were compared to those when operating on certification gasoline to determine the “success” of the conversion. Many of these conversions, performed according to the manufacturer's requirements, were not “successful” (worse emissions than for gasoline operation). In almost all cases, the problem was NOx emissions that were too high when operating on the alternative fuel.

A survey of the CNG compositions within NGV driving range of Houston was performed. It was found that the statistics for the Texas CNGs were very similar to those from a previous national survey Based upon the present survey results, two extremes of CNG composition were chosen for a study of the effects of composition on emissions, fuel economy, and driveability. Two other CNG compositions were also included to provide for comparisons with the recently completed Auto/Oil Air Quality Improvement Research Program (AQIRP) and to extend the AQIRP database. One of the vehicles used in the AQIRP study was also used in the present investigation. Correlations were investigated for the relationships between the CNG composition and tailpipe emissions, fuel economy, and driveability.

A reduced autoignition mechanism for iso-octane has been developed by identifying paths to formation of the stable species measured during motoring knock experiments and eliminating paths to formation of species that were not measured. The resulting mechanism includes low-, intermediate-, and high-temperature reactions and consists of 103 species and 131 reactions. This mechanism differs from detailed models not only in the number of reactions and species, but most importantly, in the nature and rates of the degenerate chain branching reactions. To implement this mechanism, a knock subroutine has been added to a quasidimensional spark ignition engine model that accounts for heat losses, blowby, etc. Thus, errors in the reactivity predictions can be assigned almost exclusively to the kinetics. Numerical predictions of the exhaust composition during motoring knock are compared with experimental measurements as a function of compression ratio for several operating conditions.

Because only the unburned gases in the crevices can contribute to hydrocarbon emissions, a model was developed that can be used to determine the temporal and spatial histories of both burned gas and unburned gas flow into and out of the piston-liner crevices. The burned fraction in the top-land is primarily a function of engine design. Burned gases continue to get packed into the inter-ring volume until well after the end of combustion and the unburned fuel returned to the chamber from this source depends upon both the position of the top ring end gap relative to the spark plug and of the relative positions of the end gaps of the compression rings with respect to each other. Because the rings rotate, and because the fuel that returns to the chamber from the inter-ring crevice dominates the sources between BDC and IVO when conditions are unfavorable to in-cylinder oxidation, these represent two sources of variability in the HC emissions.

Fuel transport was visualized within the cylinder of a port injected four-valve SI engine having a transparent cylinder liner. Measurements were made while motoring at 250 rpm to simulate cranking conditions prior to the first firing cycle, and at 750 rpm to examine the effects of engine speed. A production GM Quad-4 cylinder head was used, and the stock single-jet port fuel injector was used to inject indolene. A digital camera was used to capture back-lighted images of cylinder wall wetting for open and closed intake valve injection. In addition, two-dimensional planar imaging of Mie scattering from the indolene fuel droplets was used to characterize the fuel droplet distribution as a function of crank angle for open and closed intake valve injection. LDV was used to measure the droplet and air velocities near the intake valves during fuel induction. It was found that with open-valve injection a large fraction of the fuel impinged on the cylinder wall opposite the intake valves.

The Rotating Liner Engine (RLE) is an engine design concept where the cylinder liner rotates in order to reduce piston assembly friction and liner/ring wear. The reduction is achieved by the elimination of the mixed and boundary lubrication regimes that occur near TDC. Prior engines for aircraft developed during WW2 with partly rotating liners (Sleeve Valve Engines or SVE) have exhibited reduction of bore wear by factor of 10 for high BMEP operation, which supports the elimination of mixed lubrication near the TDC area via liner rotation. Our prior research on rotating liner engines experimentally proved that the boundary/mixed components near TDC are indeed eliminated, and a high friction reduction was quantified compared to a baseline engine. The added friction required to rotate the liner is hydrodynamic via a modest sliding speed, and is thus much smaller than the mixed and boundary friction that is eliminated.

The Rotating Linear Engine (RLE) derives improved fuel efficiency and decreased maintenance costs via a unique lubrication design, which decreases piston assembly friction and the associated wear for heavy-duty natural gas and diesel engines. The piston ring friction exhibited on current engines accounts for 1% of total US energy consumption. The RLE is expected to reduce this friction by 50-70%, an expectation supported by hot motoring and tear-down tests on the UT single cylinder RLE prototype. Current engines have stationary liners where the oil film thins near the ends of the stroke, resulting in metal-to-metal contact. This metal-to-metal contact is the major source of both engine friction and wear, especially at high load. The RLE maintains an oil film between the piston rings and liner throughout the piston stroke due to liner rotation. This assumption has also been confirmed by recent testing of the single cylinder RLE prototype.

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.

The Texas Department of Transportation (TxDOT) began using an ultra-low-sulfur, low aromatic, high cetane number diesel fuel (TxLED, Texas Low Emission Diesel) in June 2003. They initiated a simultaneous study of the effectiveness to reduce emissions and influence fuel economy of this fuel in comparison to 2D on-road diesel fuel used in both their on-road and off-road equipment. The study incorporated analyses for the fleet operated by the Association of General Contractors (AGC) in the Houston area. Some members of AGC use 2D off-road diesel in their equipment. One off-road engine, two single-axle dump trucks, and two tandem-axle dump trucks were tested. The equipment tested included newer electronically-controlled diesels. The off-road engine was tested over the TxDOT Telescoping Boom Excavator Cycle. The dump trucks were tested using the “route” technique over the TxDOT Single-Axle Dump Truck Cycle or the TxDOT Tandem-Axle Dump Truck Cycle.

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.

As natural gas engines are designed to operate leaner and with increased boost pressure, durability of the spark plugs becomes problematic. Among the various new ignition devices that have been considered to solve some of the problems facing spark plugs, railplugs appear to hold clear advantages in some areas. There are two types of railplugs: coaxial rail and parallel rail. This paper reports the results of an experimental study of various parameters that affect the performance of parallel railplugs. Their performance was quantified by the distance that the arc traveled along the rails from the initiation point. Travel along the rails is thought to be an important performance metric because rail-travel limits excessive local wear and produces a distributed ignition source which can potentially reduce mixture inhomogeneity induced ignition problems.

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.

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.

A design guide for vehicles is presented, including considerations of vehicle dynamics and vehicle performance. The various aspects of vehicle design are both qualitatively and quantitatively discussed, including presentation of the relevant theory, governing equations, and design options of interest for a small race car such as a Formula SAE vehicle. Relevant conclusions drawn from the theoretical analysis are presented.

This paper discusses the Formula SAE Student Engineering Design Competition that was held May 27–29, 1982. As was the case of previous student engineering design competitions, the purpose of the Formula SAE Competition is to enhance engineering education by requiring students to apply the technical knowledge gained in their coursework to a practical engineering design problem including choice of appropriate design criteria, design, fabrication, testing, and evaluation. For the Formula SAE Competition, the design problem chosen is to design, construct, and compete a low powered Indianapolis-type race car. The purpose of this paper is to describe the 1982 Formula SAE Competition and to present the results of this event. It is expected that this paper will serve as a guide to hosts of similar competitions and will aid future Formula SAE competitors.