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Technical Paper

Liquid Film Evaporation Off the Piston of a Direct Injection Gasoline Engine

2001-03-05
2001-01-1204
An optical access engine was used to image the liquid film evaporation off the piston of a simulated direct injected gasoline engine. A directional injector probe was used to inject liquid fuel (gasoline, i-octane and n-pentane) directly onto the piston of an engine primarily fueled on propane. The engine was run at idle conditions (750 RPM and closed throttle) and at the Ford World Wide Mapping Point (1500 RPM and 262 kPa BMEP). Mie scattering images show the liquid exiting the injector probe as a stream and directly impacting the piston top. Schlieren imaging was used to show the fuel vaporizing off the piston top late in the expansion stroke and during the exhaust stroke. Previous emissions tests showed that the presence of liquid fuel on in-cylinder surfaces increases engine-out hydrocarbon emissions.
Technical Paper

The Effects of Fuel Volatility and Structure on HC Emissions from Piston Wetting in DISI Engines

2001-03-05
2001-01-1205
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. All of our prior tests with the injector probe used California Phase 2 reformulated gasoline as the liquid fuel. In the present study, a variety of pure liquid hydrocarbon fuels are used to examine the influence of fuel volatility and structure. Additionally, the exhaust hydrocarbons are speciated to differentiate between the emissions resulting from the gaseous fuel and those resulting from the liquid fuel. It is 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.
Technical Paper

Particulate Characterization of a DISI Research Engine using a Nephelometer and In-Cylinder Visualization

2001-05-07
2001-01-1976
A nephelometer system was developed to characterize engine particulate emissions from DISI engines. Results were correlated with images showing the location and history of particulates in the cylinder of an optical engine. The nephelometer's operation is based upon the dependence of scattered laser light on particulate size from a flow sampled from the exhaust of an engine. The nephelometer simultaneously measured the scattered light from angles of 20° to 160° from the forward scattering direction in 4° increments. The angular scattering measurements were then compared with calculations using a Mie scattering code to infer information regarding particulate size. Measurements of particulate mass were made based upon a correlation developed between the scattered light intensity and particulate mass samples trapped in a 0.2-micron filter. Measurements were made in a direct injection single-cylinder spark ignition research engine having a transparent quartz cylinder.
Technical Paper

Effects of Fuel Volatility, Load, and Speed on HC Emissions Due to Piston Wetting

2001-05-07
2001-01-2024
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.
Technical Paper

Refinement of a Dedicated E85 1999 Silverado with Emphasis on Cold Start and Cold Drivability

2001-03-05
2001-01-0679
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.
Technical Paper

Conversion of a 1999 Silverado to Dedicated E85 with Emphasis on Cold Start and Cold Driveability

2000-03-06
2000-01-0590
The University of Texas Ethanol Vehicle Challenge team focused upon cold start/driveability, fuel economy, and emissions reduction for our 1999 Ethanol Vehicle Challenge entry. We replaced or coated all fuel system components that were not ethanol compatible. We used the stock PCM for all control functions except control of a novel 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, increased EGR for the operating conditions of the five longest cruises on the FTP, and our cold-start system that eliminates the need to overfuel the engine at the beginning of the FTP. This EGR control scheme should also benefit urban fuel economy. Additionally, we eliminated EGR at high load to improve power density.
Technical Paper

Development and Application of an Improved Ring Pack Model for Hydrocarbon Emissions Studies

1996-10-01
961966
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.
Technical Paper

The Texas Project, Part 4 - Final Results: Emissions and Fuel Economy of CNG and LPG Conversions of Light-Duty Vehicles

1998-10-19
982446
The Texas Project was a multi-year study of aftermarket conversions of a variety of light-duty vehicles to CNG or LPG. Emissions and fuel economy when using these fuels are compared to the results for the same vehicles operating on certification gasoline and Federal Phase 1 RFG. Since 1993, 1,040 tests were conducted on 10 models, totally 86 light-duty vehicles. The potential for each vehicle model/kit combination to attain LEV certification was assessed. Also, comparisons of emissions and fuel economy between converted vehicles when operating on gasoline and nominally identical un-converted gasoline control vehicles were analyzed. Additional evaluations were performed for a subfleet that was subjected to exhaust speciations for operation over the Federal Test Procedure cycle and also for off-cycle tests.
Technical Paper

The Effects of Fuel Composition, System Design, and Operating Conditions on In-System Vaporization and Hot Start of a Liquid-Phase LPG Injection System

1998-05-04
981388
A liquid-phase port injection system for liquefied petroleum gas (LPG) generally consists of a fuel storage tank with extended capability of operating up to 600 psi, a fuel pump, and suitable fuel lines to and from the LPG fuel injectors mounted in the fuel rail manifold. Port injection of LPG in the liquid phase is attractive due to engine emissions and performance benefits. However, maintaining the LPG in the liquid phase at under-hood conditions and re-starting after hot soak can be difficult. Multiphase behavior within a liquid-phase LPG injection system was investigated computationally and experimentally. A commercial chemical equilibrium code (ASPEN PLUS™) was used to model various LPG compositions under operating conditions.
Technical Paper

Diluents and Lean Mixture Combustion Modeling for SI Engines with a Quasi-Dimensional Model

1995-10-01
952382
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.
Technical Paper

The Texas Project: Part 3 - Off-Cycle Emissions of Light-Duty Vehicles Operating on CNG, LPG, Federal Phase 1 Reformulated Gasoline, and/or Low Sulfur Certification Gasoline

1996-10-01
962100
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
Technical Paper

Combustion Modeling in SI Engines with a Peninsula-Fractal Combustion Model

1996-02-01
960072
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.
Technical Paper

The Texas Project: Part 1 - Emissions and Fuel Economy of Aftermarket CNG and LPG Conversions of Light-Duty Vehicles

1996-10-01
962098
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.
Technical Paper

The Texas Project: Part 2 - Control System Characteristics of Aftermarket CNG and LNG Conversions for Light-Duty Vehicles

1996-10-01
962099
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.
Technical Paper

CNG Compositions in Texas and the Effects of Composition on Emissions, Fuel Economy, and Driveability of NGVs

1996-10-01
962097
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.
Technical Paper

Mixture Preparation During Cranking in a Port-Injected 4-Valve SI Engine

1997-10-01
972982
This paper presents the results of an experimental investigation of the fuel-air mixing process in a port-fuel-injected, 4-valve, spark-ignited engine that was motored to simulate cold cranking and start-up conditions. An infrared fiber-optic instrumented spark plug probe was used to measure the local, crank angle resolved, fuel concentration in the vicinity of the spark gap of a single-cylinder research engine with a production head and fuel injector. The crank-angle resolved fuel concentrations were compared for various injection timings including open-intake-valve (OIV) and closed-intake-valve (CIV) injection, using federal certification gasoline. In addition, the effects of speed, intake manifold pressure, and injected fuel mass were examined.
Technical Paper

Condensation of Fuel on Combustion Chamber Surfaces as a Mechanism for Increased HC Emissions from SI Engines During Cold Start

1997-10-01
972884
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.
Technical Paper

Initial Studies of a New Type of Ignitor: The Railplug

1991-10-01
912319
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.
Technical Paper

Investigation of a Novel Aid for Cold Starting of Diesels

1989-02-01
890041
An experimental investigation of the use of an engine coolant exchange system for prewarming diesel engines before cold starting is discussed. This coolant exchange system involves connecting the coolant system of a fully warmed-up and running engine (e.g., a spark ignition engine) to that of the cold diesel to be started using hydraulic hoses with quick connect fittings and an auxiliary pump. The investigation was performed using a 4,3 liter V6 indirect injection diesel engine since this represents a difficult case for cold starting. The starting characteristics using the coolant exchange technique are compared to those using the production glow plug system, which includes a fuel heater and afterglow. It is shown that the coolant exchange system allows this engine to be started down to −26 °C, much colder than the −13°C limit for the production glow plug system.
Technical Paper

Development of a Computationally Fast Equilibrium-Equivalent 4-Stroke SI Engine Model

1988-02-01
880130
A set of algebraic equations has been developed to replace the iterative thermochemical equilibrium subroutine in zero-dimensional and quasidimensional engine modeling codes. These equations allow calculation of the equilibrium composition given only the equivalence ratio and the fuel characteristics, thereby allowing the composition calculations to be performed external to the iterative main loop. This technique results in a decrease of the required computational time by up to a factor of 13, dependent upon the equivalence ratio and the fuel. The predictions of the equilibrium-equivalent code agree with those of a traditional equilibrium code within 2.5% for the four fuels examined (CH4, C3H8, C2H5OH, and i-C8H18) for compression ratios between 5 and 12:1, intake manifold pressures between 50 and 100 kPa, and equivalence ratios from 0.5 to 1.5. A technique for including constrained equilibrium to account for freezing of CO oxidation during the expansion stroke is also presented.
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