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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.

Initial investigations of a new type of high energy ignitor for I.C. engines are described. The ignitor is a miniaturized railgun, or “railplug.” The railplug produces a relatively large mass of high velocity plasma. These characteristics may be advantageous for initiating combustion in a number of different applications. Unlike a plasma jet ignitor, the railplug plasma is driven not only by thermodynamic expansion, but by electromagnetic forces as well. Four experimental railplug designs were evaluated using schlieren and shadowgraphy visualization to examine plasma movement and shape. Railplug current and voltage were also measured. One railplug consisting of two unenclosed parallel rails was used to demonstrate the electromagnetically induced motion of the plasma at ambient conditions. Schlieren photos showed that the plasma plume moves strongly in the direction of the electromagnetic Lorentz forces.

Condensation of fuel vapor on the cold surfaces within the combustion chamber is investigated as a possible mechanism for increased HC emissions from SI engines during cold start. A one-dimensional, transient, mass diffusion analysis is used to examine the condensation of single-species fuels on the surfaces of the combustion chamber as the pressure within the cylinder rises during compression and combustion, and re-vaporization during expansion, blowdown, and exhaust. The effects of wall temperature, fuel volatility, and engine load and speed on this mechanism are also discussed. This analysis shows that low-volatility fuel components can condense on the surfaces of the combustion chamber when the surface temperatures are sufficiently low. This condensed fuel may re-vaporize during the power and exhaust strokes, or it may remain in the combustion chamber until surface temperatures rise, perhaps tens of seconds later.

Combustion chamber pressure measurement in engines via a passage is an old technique that is still widely used in engine research. This paper presents improved passage designs for an off-set electrode spark plug designed to accept a pressure transducer. The spark plug studied was the Champion model 304-063A. Two acoustic models were developed to compute the resonance characteristics. The new designs have a resonance frequency in a range higher than the fundamental frequency expected from knock so that the signal can be lowpass filtered to remove the resonance and not interfere with pressure signal components associated with combustion phenomena. Engine experiments verified the spark plug resonance behavior. For the baseline engine operating condition approximately 50 of 100 cycles had visible passage resonance in the measured pressure traces, at an average frequency of 8.03 kHz.

A review of flame kernel growth in SI engines and the regimes of premixed turbulent combustion showed that a misfire model based on regimes of premixed turbulent combustion was warranted[1]. The present study will further validate the misfire model and show that it has captured the dominating physics and avoided extremely complex, yet inefficient, models. Results showed that regimes of turbulent combustion could, indeed, be used for a concept-simple model to predict misfire limits in SI engines. Just as importantly, the entire regimes of premixed turbulent combustion in SI engines were also mapped out with the model.

Trucks operating in inter-modal (drayage) operation in and around port and rail terminals, are responsible for a large proportion of the emissions of NOX, which are problematic for the air quality of the Houston and Dallas/Ft. Worth metro areas. A standard test cycle, called the Texas Dray Truck Cycle, was developed to represent the operation of heavy-duty diesel trucks in dray operations. The test cycle reflects the substantial time spent at idle (~45%) and the high intensity of the on-road portions. This test cycle was then used in the SAE J1321 test protocol to evaluate the effect on fuel consumption and NOX emissions of retrofitting dray trucks with light-weight, low-rolling resistance wide-single tires. In on-track testing, a reduction in fuel consumption of 8.7% was seen, and NOX emissions were reduced by 3.8% with the wide single tires compared to the conventional tires.

The Texas Department of Transportation began using an emulsified diesel fuel in 2002. They initiated a simultaneous study of the effectiveness of this fuel in comparison to 2D on-road diesel fuel and 2D off-road diesel. The study included comparisons of fuel economy and emissions for the emulsion, Lubrizol PuriNOx®, relative to conventional diesel fuels. Two engines and eight trucks, four single-axle dump trucks, and four tandem-axle dump trucks were tested. The equipment tested included both older mechanically-controlled diesels and newer electronically-controlled diesels. The two engines were tested over two different cycles that were developed specifically for this project. The dump trucks were tested using the “route” technique over one or the other of two chassis dynamometer cycles that were developed for this project In addition to fuel efficiency, emissions of NOx, PM, CO, and HCs were measured. Additionally, second-by-second results were obtained for NOx and HCs.

Ethanol is one of many alternative transportation fuels that can be burned in internal combustion engines in the same ways as gasoline and diesel. Compared to hydrogen and electric energy, ethanol is very similar to gasoline in many aspects and can be delivered to end-users by the same infrastructures. It can be produced from biomass and is considered renewable. It is expected that the improvement in fuels over the next 20 years will be by blending biomass-based fuels with fossil fuels using existing technologies in present-day automobiles with only minor modifications, even though the overall costs of using biomass-based fuels are still considerably higher than conventional fuels. Ethanol may represent a significant alternative fuel source, especially during the transition from fossil-based fuels to more exotic power sources. Mapping engines for flexible fuel vehicles (FFV), however, would be very costly and time consuming, even with the help of model-based engine mapping (MBM).

In order to determine the factors that affect fuel economy quantitatively, the power flows through the major powertrain components were measured during operation over transient cycles. The fuel consumption rate and torque and speed of the engine output and axle shafts were measured to assess the power flows in a vehicle with a CVT. The measured power flows were converted to energy loss for each component to get the efficiency. Tests were done at Phase 1 and Phase 3 of the FTP and for two different CVT shift modes. The measured energy distributions were compared with those from the ADVISOR simulation and to results from the PNGV study. For both the Hot 505 and the Cold 505, and for both shift modes, the major powertrain loss occurs in the engine, including or excluding standby losses. However, the efficiency of the drivetrain/transmission is important because it influences the efficiency of the engine.

Improved submodels for use in a dynamic engine/vehicle model have been developed and the resulting code has been used to analyze the tip-in, tip-out behavior of a computer-controlled port fuel injected SI engine. This code consists of four submodels. The intake simulation submodel is similar to prior intake models, but some refinements have been made to the fuel flow model to more properly simulate a timed port injection system, and it is believed that these refinements may be of general interest. A general purpose engine simulation code has been used as a subroutine for the cycle simulation submodel. A conventional vehicle simulation submodel is also included in the model formulation. Perhaps most importantly, a submodel has been developed that explicitly simulates the response of the on-board computer (ECM) control system.

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.

Powertrain and vehicle technology is rapidly changing to meet the ever increasing demands of customers and government regulations. In some cases technologies that are designed to improve one attribute may impact others or interact with other design decisions in unexpected ways. Understanding the interactions and optimizing the transient performance at the vehicle level may require controls and calibration that is not available until late in the vehicle development process, after hardware changes are no longer possible. As a result, an efficient, up front, CAE process for assessing the interaction of various design choices on transient vehicle behavior is desirable. Building, calibrating and validating a vehicle system model with full controls and a mature calibration is very time consuming and often requires significant experimental data that is not available until it is too late to make hardware changes.

Predictions of the Fractal Engine Simulation code were compared with SI engine data in a previous paper. These comparisons were extremely good except for the single data set available at a low engine speed. Because of uncertainty regarding whether the lack of agreement for this case resulted from some difficulty with the experimental data or was due to lack of proper speed dependence in the model, additional comparisons are made for a range of speeds from 300-1500 rpm. The fractal burning model is a turbulence driven model (i.e., driven primarily by the turbulence intensity) that divides the combustion process into four sequential phases: 1) kernel formation, 2) early flame growth, 3) fully developed turbulent flame propagation, and 4) end of combustion. The kernel formation process was not included in the previous version of this model, but was found to be required to predict engine speed effects.

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.

Electronic control of valve timing and event duration in a camless engine enables the optimization of fuel economy, performance, and emissions at each engine operating condition. This flexible engine technology can offer significant benefits to each of these areas, but optimization techniques become crucial to achieving these benefits and understanding the principles behind them. Optimization techniques for an I4 - 2.0L camless ZETEC dynamometer engine have been developed for a variety of areas including: Cold Starts Cylinder Deactivation Full Load Idle Transient A/F control The procedure for the optimization of each of these areas will be presented in detail, utilizing both steady state and transient dynamometer testing. Experimental data will be discussed and the principles governing the response of the engine will be explained. Selection criteria for determining an optimum strategy for the different modes will be presented and recommendations will be discussed.

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.

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.

Tumble flow has been recognized as an important and positive enhancement of combustion for SI engines. Tumble flow modeling with quasi-dimensional models is difficult because of the transient nature of tumble vortex, compared with swirl flows. Although multi-dimensional models have obtained plenty of attention recently in engine research, quasi-dimensional SI engine models will continue to dominate industrial applications in the near future. In the present research, a bulk flow model has been developed for tumble flows based on angular momentum conservation. Its effect on turbulence was then modeled using a Two-Equation Model (k-ε Model). A methodology has also been developed to use particle tracking velocimetry (PTV) measurement to calibrate the quasi-dimensional bulk flow model at engine BDC to model tumble vortex and tumble-generated turbulence. The Entrainment Combustion Model was used for combustion modeling.