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Optimization of the engine cold start is critical for gasoline direct injection (GDI) engines to meet increasingly stringent emission regulations, since the emissions during the first 20 seconds of the cold start constitute more than 80% of the hydrocarbon (HC) emissions for the entire EPA FTP75 drive cycle. However, Direct Injection Spark Ignition (DISI) engine cold start optimization is very challenging due to the rapidly changing engine speed, cold thermal environment and low cranking fuel pressure. One approach to reduce HC emissions for DISI engines is to adopt retarded spark so that engines generate high heat fluxes for faster catalyst light-off during the cold idle. This approach typically degrades the engine combustion stability and presents additional challenges to the engine cold start. This paper describes a CFD modeling based approach to address these challenges for the Ford 3.5L V6 EcoBoost engine cold start.

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 (Multi-dimensional 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.

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.

The physics of the mixture preparation process plays a critical role in transient engine control, a key enabler for satisfying increasingly stringent emissions requirements. This paper presents a fully transient, coupled model in Modelica for the liquid fuel behavior and thermodynamic engine cycle including thermal effects for a port fuel injection engine. Details of both the liquid fuel transport and cycle simulation models are provided. The integrated model is used to examine the effects of variable cam timing on the transient fuel behavior including comparisons between simulation results and experimental data under a variety of engine operating conditions.

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.

A technique was developed for measuring the Laminar Burning Velocity (LBV) of multi-component fuel blends for use in high-performance spark-ignition engines. This technique involves the use of a centrally-ignited spherical combustion chamber, and a complementary analysis code. The technique was validated by examining several single-component fuels, and the computational procedure was extended to handle multi-component fuels without requiring detailed knowledge of their chemical composition. Experiments performed on an instrumented high-speed engine showed good agreement between the observed heat-release rates of the fuels and their predicted ranking based on the measured LBV parameters.

The University of Texas 2000 Ethanol Vehicle Challenge team remains focused on cold start, cold drivability, fuel economy, and emissions reduction for our 2000 Ethanol Vehicle Challenge entry. We used the stock PCM for all control functions except control of an innovative cold-start system our team designed. The primary modifications for improved emissions control involved ceramic coating of the exhaust manifolds, use of close-coupled ethanol-specific catalysts, use of a moddified version of the California Emissions Calibrated PCM, and our cold-start system that eliminates the need to overfuel the engine at the beginning of the FTP. Additionally, we eliminated EGR at high load to improve power density. Major modifications, such as increasing the compression ratio or pressure boosting, were eliminated from consideration due to cost, complexity, reliability, or emissions penalties.

The impingement of liquid fuel onto the surfaces of the combustion chamber (wall-wetting) has been shown to be an important source of HC emissions from direct-injected SI engines, and can even result in pool fires and diffusion flames. Some degree of wall wetting, particularly on the piston top, is believed to occur in every current DIG engine design, but the behavior of the wall-bound fuel throughout the engine cycle is poorly understood. The goal of this study was to gain a better understanding of the fundamental interaction between liquid fuel droplets and the piston under engine-like conditions, by observing the vaporization of individual fuel drops as the surface temperature and ambient pressures were varied in a controlled environment. The vaporization of several single-component fuels, binary mixtures, and multi-component fuels was examined in the range of surface temperatures between 50 and 300 °C and ambient pressures between 50 and 1270 kPa (abs).

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.

Motor vehicle hydrocarbon evaporative emissions are a crucial part of emissions regulations, and increasingly-stringent regulations stipulate essentially zero fuel-based hydrocarbon evaporative emissions. In port fuel injected engines, there is the potential for accumulation of PCV effluent in the intake system under certain vehicle operating conditions. The majority of this effluent is oil, but a percentage has been shown to be fuel. The percentage of fuel in this oil-fuel mixture in the intake is at a minimum equivalent to the fuel dilution level of the crankcase oil, and at times can be higher due to other sources of fuel, and fuel vapor, in the intake. This accumulation of liquid oil-fuel mixture can be a contributor of hydrocarbon evaporative emissions migrating out of the air induction system when subjected to transient temperatures while the engine is off.

EmiSense Technologies, LLC (www.emisense.com) is commercializing its electronic particulate matter (PM) sensor that is based on technology developed at the University of Texas at Austin (UT). To demonstrate the capability of this sensor for real-time PM measurements and on board diagnostics (OBD) for failure detection of diesel particle filters (DPF), independent measurements were performed to characterize the engine PM emissions and to compare with the PM sensor response. Computational fluid dynamics (CFD) modeling was performed to characterize the hydrodynamics of the sensor's housing and to develop an improved PM sensor housing with reproducible hydrodynamics and an internal baffle to minimize orientation effects. PM sensors with the improved housing were evaluated in the truck exhaust of a heavy duty (HD) diesel engine tested on-road and on a chassis dynamometer at the University of California, Riverside (UCR) using their Mobile Emissions Laboratory (MEL).

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.

A large amount of the heat generated during the engine combustion process is lost to the coolant system through the surrounding metal parts. Therefore, there is a potential to improve the overall cycle efficiency by reducing the amount of heat transfer from the engine. In this paper, a Computational Fluid Dynamics (CFD) tool has been used to evaluate the effects of a number of design and operating variables on total heat loss from an engine to the coolant system. These parameters include injection characteristics and orientation, shape of the piston bowl, percentage of EGR and material property of the combustion chamber. Comprehensive analyses have been presented to show the efficient use of the heat retained in the combustion chamber and its contribution to improve thermal efficiency of the engine. Finally, changes in design and operating parameters have been suggested based on the analytical results to improve heat loss reduction from an engine.

Advancing intake valve timing shortly after engine crank and run-up can potentially reduce vehicle cold start hydrocarbon (HC) emissions in port fuel injected (PFI) engines equipped with intake variable cam timing (iVCT). Due to the cold metal temperatures, there can be significant accumulation of liquid fuel in the intake system and in the cylinder. This accumulation of liquid fuel provides potential sources for unburned hydrocarbons (HCs). Since the entire vehicle exhaust system is cold, the catalyst will not mitigate the release of unburned HCs. By advancing the intake valve timing and increasing valve overlap, liquid fuel vaporization in the intake system is enhanced thereby increasing the amount of burnable fuel in the cylinder. This increase in burnable HCs must be countered by a reduction in injector-delivered fuel via a compensator that reacts to cam movement.

Multi-dimensional numerical simulation of the combustion process in spark ignition engines were performed using the Coherent Flame Model (CFM) which is based on the flamelet assumption. The CFM uses a balance equation for the flame surface area to simulate flame surface advection, diffusion, production and destruction in a turbulent reacting flow. There are two model constants in CFM, one associated with the modeling of flame surface production and the other with the modeling of flame surface destruction. Previous experimental results on two test engines charged with propane-air mixtures were used to compare with the computations for different engine speeds, loads, equivalence ratios and spark plug locations. Predicted engine cylinder pressure histories agree well with the experimental results for various operating conditions after the model constants were calibrated against a reference operating condition.

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 of plasma. Additionally, railplugs have the potential of assuring ignition under adverse conditions, such as cold start of an IDI diesel engine, because the railplug plasma can force ignition in the combustion chamber rather than relying on autoignition under cold start conditions. In this paper, engine data are presented to demonstrate the improved cold starting capability obtainable with railplugs. Data acquired using a railplug are compared to results obtained using no assist and using glow plugs. The engine used for this investigation will not start without glow plugs (or some starting aid) at temperatures below O°C, and the manufacturer's specification of the cold start limit for this engine using glow plugs is -24°C. Railplugs are able to initiate combustion at -29°C in one to two seconds with no preheating.

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.