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A multi-dimensional cathode spot generation model is proposed to study the interaction between the plasma arc and cathode surface of a spark plug during the ignition process. The model is focused on the instationary (high current) arc phase immediately following breakdown, and includes detailed physics for the phenomena during spot formation such as ion collision, thermal-field emission, and metal vaporization, to simulate the surface heat source, current density and surface pressure. The spot formation for a platinum cathode is simulated using the VOF (volume of fluid) model within FLUENT, where the local metal is melted and deformed by pressure differences on the surface. A random walk model has been integrated to consider the movement of the arc center, resulting in the formation of different types of spots.

An experimental study of the spark ignition process for SI engines was conducted to study spark plug erosion and the effect of breakdown voltage/energy on electrode surface deformation. The experiments were conducted outside of an engine, in both a pressurized constant volume optical chamber and in a high-pressure vessel heated within a furnace with gas temperatures as high as 730°C. J-gap spark plugs designed for natural gas engines were studied at elevated temperature and under a range of pressures to investigate electrode wear characteristics. Both iridium-alloy and platinum-alloy cathode (center electrode) and anode (ground strap) spark plugs were investigated. In addition, single spark events were performed on polished platinum cathode surfaces to allow the visualization of craters from individual spark events in order to quantify how their size and shape were affected by energy deposition and breakdown characteristics.

A multi-dimensional model of the spark ignition process for SI engines was developed as a user defined function (UDF) integrated into the commercial engine simulation software CONVERGE CFD. The model simulates spark plasma movement in an inert flow environment without combustion. The UT model results were compared with experiments for arc movement in a crossflow and also compared with calorimeter measurements of thermal energy deposition under quiescent conditions. The arc motion simulation is based on a mean-free-path physical model to predict the arc movement given the contours of the crossflow velocity through the gap and the interaction of the spatially resolved electric field with the electrons making up the arc. A further development is the inclusion of a model for the thermal energy deposition of the arc as it is stretched by the interaction of the flow and the electric field.

Spark discharge properties were studied and characterized for varying gas compositions and spark plug geometries using a spark calorimeter and constant volume optical vessel. Two different 18 mm natural gas engine spark plugs were used in the experiments. All measurements were recorded under quiescent conditions and with a spark gap of 0.30 mm. The spark plug calorimeter was used for measuring thermal energy deposition to the gas for gas compositions of nitrogen, a stoichiometric mixture of nitrogen and methane, a stoichiometric mixture of nitrogen and methane diluted with 30% carbon dioxide by volume, and for air. Other measurements of interest included breakdown voltage, electrical energy delivered to the spark gap, electrical-to-thermal energy conversion efficiency, and spark duration, for pressures up to 28 bar at 300 K. The optical vessel was used for the combusting mixture of stoichiometric air and methane at pressures up to 28 bar.

The arc characteristics and discharge behavior of a representative inductive spark ignition system were characterized with a spark plug calorimeter and a constant volume vessel used to create high-pressure crossflow velocities through the gap of the spark plug. A 14 mm diameter natural gas engine spark plug was used for the measurements. The discharges were into a non-combusting gas, primarily nitrogen. The spark plug calorimeter was used to determine the electrical-to-thermal energy conversion in the spark gap under quiescent conditions, while the constant volume vessel was used to study ignition arc structure in convective crossflows and imaged with a high-speed camera. Topics included the effect of crossflow velocity, pressure (up to 20 bar at 300 K), and gap distance on breakdown voltage, arc duration and delivered electrical energy. Also of interest was the amount of remaining electrical energy on the coil versus spark duration in a cross flow.

A multi-dimensional model of the spark ignition process for SI engines was developed as a user defined function (UDF) integrated into the commercial engine simulation software CONVERGE™ CFD. For the present research, the model simulated spark plasma development in an inert flow environment without combustion. The UT model results were then compared with experiments. The UT CONVERGE CFD-based model includes an electrical circuit sub-model that couples the primary and secondary sides of an inductive ignition system to predict arc voltage and current, from which the transient delivered electrical energy to the gap can be determined. Experimentally measured values of the arc resistance and spark plug calorimeter measurements of the efficiency of electrical to thermal energy conversion in the gap were used to determine the thermal energy delivered to the gas in the spark gap for different pressures and gap distances.

Spark plug electrode heat transfer and its relationship with the thermal energy deposition from the spark plasma to the gas in the spark gap was studied under quiescent non-combusting conditions. The thermal energy deposition to the gas (N2) was measured with a spark plug calorimeter as a function of pressure, up to 30 bar. The measurements were carried out for two gap distances of 0.3 mm and 0.9 mm, for three nominally identical spark plugs having different electrode surface area and/or surface thermal conductivity. The unmodified baseline spark plug had a nickel center electrode (cathode) 2.0 mm in diameter, the first modified spark plug had both the ground and center electrodes shaved to a diameter of approximately 0.5 mm, and the second modified spark plug had copper inserts bonded to both electrodes. The experimental results were compared with multi-dimensional simulations of the conjugate heat transfer to the gas and to the metal electrodes, conducted using CONVERGE CFD.

A series of cold start experiments using a 2.0 liter gasoline turbocharged direct injection (GTDI) engine with custom controls and calibration were carried out using gasoline and iso-pentane fuels, to obtain the cold start emissions profiles for the first 5 firing cycles at an ambient temperature of 22°C. The exhaust gases, both emitted during the cold start firing and emitted during the cranking process right after the firing, were captured, and unburned hydrocarbon emissions (HC), CO, and CO2 on a cycle-by-cycle basis during an engine cold start were analyzed and quantified. The HCs emitted during gasoline-fueled cold starts was found to reduce significantly as the engine cycle increased, while CO and CO2 emissions were found to stay consistent for each cycle. Crankcase ventilation into the intake manifold through the positive-crankcase ventilation (PCV) valve system was found to have little effect on the emissions results.

The continuing growth of urban population centers has led to increased traffic congestion for which vehicles can spend considerable periods at low speed/low load and idle conditions. For light-duty diesel vehicles, these low load conditions are characterized by low engine exhaust temperatures (~100oC). Exhaust temperatures can be too low to maintain the activity of the catalytic exhaust aftertreatment devices (usually need >~200oC) which can lead to high emissions that contribute to deteriorating urban air quality. This study is a follow-on to two previous studies on the effects of throttling, post-injection, and cylinder deactivation (CDA) on light-duty diesel engine exhaust temperatures and emissions. The focus of the present study is on fuel consumption, exhaust temperatures, and emissions with and without cylinder deactivation or with fuel cutout, and the sensitivity to or effects of fuel rail pressure, along with observations of apparent idle engine friction.

There is keen interest in understanding the origins of engine-out unburned hydrocarbons emitted during SI engine cold start. This is especially true for the first few firing cycles, which can contribute disproportionately to the total emissions measured over standard drive cycles such as the US Federal Test Procedure (FTP). This study reports on the development of a novel methodology for capturing and quantifying unburned hydrocarbon emissions (HC), CO, and CO2 on a cycle-by-cycle basis during an engine cold start. The method was demonstrated by applying it to a 4 cylinder 2 liter GTDI (Gasoline Turbocharged Direct Injection) engine for cold start conditions at an ambient temperature of 22°C. For this technique, the entirety of the engine exhaust gas was captured for a predetermined number of firing cycles.

The Rotating Liner Engine (RLE) concept is a design concept for internal combustion engines, where the cylinder liner rotates at a surface speed of 2-4 m/s in order to assist piston ring lubrication. Specifically, we have evidence from prior art and from our own research that the above rotation has the potential of eliminating the metal-to-metal contact/boundary friction that exists close to the piston reversal areas. This frictional source becomes a significant energy loss, especially in the compression/expansion part of the cycle, when the gas pressure that loads the piston rings and skirts is high. This paper describes the Diesel RLE prototype constructed from a Cummins 4BT and the preliminary observations from initial low load testing. The critical technical challenge, namely the rotating liner face seal, appears to be operating with negligible gas leakage and within the hydrodynamic lubrication regime for the loads tested (peak cylinder pressures of the order of 80 bar).

To perform coastdown tests on heavy-duty trucks, both long acceleration and coasting distances are required. It is very difficult to find long flat stretches of road to conduct these tests; for a Class 8 truck loaded to 80,000 lb, about 7 miles of road is needed to complete the coastdown tests. In the present study, a method for obtaining coastdown coefficients from data taken on a road of variable grade is presented. To this end, a computer code was written to provide a fast solution for the coastdown coefficients. Class 7 and Class 8 trucks were tested with three different weight configurations: empty, “cubed-out” (fully loaded but with a payload of moderate density), and “weighed-out” (loaded to the maximum permissible weight).

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).

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.

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.

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.

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.

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.