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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.

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.

A new electronic sensor has been developed to measure the time-resolved concentration of carbonaceous particulate matter (PM) emitted in engine exhaust. One application of the sensor could be to provide cycle-resolved feedback on the carbonaceous PM concentration in the exhaust to the engine control unit (ECU), thereby enabling real-time control of engine operating parameters to lower PM emissions. Another promising application is to monitor the performance of particulate traps. The sensor was tested in exhaust flows from a single cylinder diesel engine and from a steady-state acetylene diffusion flame in a flow tunnel. Steady-state engine measurements were made at constant speed and variable load, and transient measurements were performed during engine start-up and accelerations. The sensor response was compared with an opacity meter and with gravimetric filter measurements.

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.

A piezoelectric sensor to measure the mass of fuel that impacts the piston top during injection in a direct injection spark ignition (DISI) engine was developed. The sensor used a 3.18 cm (1.25-inch) long, 0.318 cm (0.125-inch) wide piezo bending motor. The principle of operation is based on the change in natural vibration frequency that occurs to the cantilever piezo beam due to a change in its mass caused by the presence of liquid fuel on its surface. An electrical impulse is used to set the piezo element in vibration after which the natural vibrational frequency is measured using a FFT analyzer. The concept was evaluated outside the engine and calibrated for the frequency shift as a function of the weight of liquid on the bending element. The change in the frequency was found to be approximately proportional to the liquid mass on the sensor. The piston top of the engine was modified to accommodate the sensor on its surface.

The cold start process is critical to control the emissions in a gasoline direct injection (GDI) engine. However, the optimization is very challenging due to the transient behavior of the engine cold start. A series of engine simulations using CONVERGE CFD™ were carried out to show the detailed process in the very first firing event of a cold start. The engine operating parameters used in the simulations, such as the transient engine speed and the fuel rail pressure (FRP), came from companion experiments. The cylinder pressure traces from the simulations were compared with experiments to help validate the simulation model. The effects of variation of the transient parameters on in-cylinder mixture distribution and combustion are presented, including the effects of the rapidly changing engine speed, the slowly vaporized fuel due to the cold walls, and the low FRP during the first firing cycle of a 4-cylinder engine. Comparison was also made with non-transient steady state operation.

An On-Board Distillation System (OBDS) was developed to extract, from gasoline, a highly volatile crank fuel that allows the reduction of startup fuel enrichment and significant spark retard during cold starts and warm-up. This OBDS was installed on a 2001 Lincoln Navigator to explore the emissions reductions possible on a large vehicle with a large-displacement engine. The fuel and spark calibration of the PCM were modified to exploit the benefits of the OBDS startup fuel. Three series of tests were performed: (1) measurement of the OBDS fuel composition and distillation curve per ASTM D86, (2) measurement of real-time cold start (20 °C) tailpipe hydrocarbon emissions for the first 20 seconds of engine operation, and (3) FTP drive cycles at 20 °C with engine-out and tailpipe emissions of gas-phase species measured each second. Baseline tests were performed using stock PCM calibrations and certification gasoline.

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.

Laminar flow elements (LFEs) are commonly used to measure the flow rate of gases in various flow streams. Since LFEs operate on the principle of fully developed laminar pipe flow, the viscosity of the gas must be known. In many cases, the flowing gas is air of varying humidity, inlet temperature, and inlet pressure. While the viscosity of humid air has been studied extensively over the past 60+ years, the effects of humidity have not been consistently accounted for in the literature and industry documentation pertaining to LFE operation, and this can lead to errors. Additionally, the available LFE operational documentation is not presented in equation form; rather it is provided in tables and graphs which do not facilitate automation of the flow calculations during data acquisition. This paper provides a brief review of the available data and correlations for the viscosity of humid air and its application to the calculation of air flow rate using a laminar flow element.

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).

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.

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 study extends a previous study on the effects of intake throttling and post-injection on light-duty Diesel engine exhaust temperatures and emissions, and includes the effects of EGR, in-cylinder swirl air motion, and cylinder deactivation. The baseline injection strategy was adapted from a 2014 Chevrolet Cruze having an engine similar to the light-duty GM engine used for this study. While the engine was fixed to a motoring engine dynamometer, the dynamometer was not active for the study, as the engine was operated under idle conditions. The desired idle speed was controlled using a feedback loop in the control algorithm to vary the duration of the main injection event. Three methods were investigated. In the first method, the engine was operated fully warmed up, firing all four cylinders.

A fiber optic instrumented spark plug was used to make time-resolved measurements of the fuel vapor concentration history near the spark gap in a four-valve DISI engine. Four different bulk flow were investigated. Several early and late injection timings were examined. The fuel concentration at the spark gap was correlated with IMEP. Emissions of CO, HCs, and NOx were related to the type of bulk flow. For both early and late injection the CoVs of fuel concentration were generally lowest for the weakest bulk flow which resulted in a stable stratification. Strong bulk flows convected the inhomogeneities through the measurement area near the spark plug resulting in both large intracycle and cycle-to-cycle variation in equivalence ratio at the time of ignition.

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.

We have examined the influence of piston wetting on the size distribution and mass of particulate matter (PM) emissions in a SI engine using several different fuels. Piston wetting was isolated as a source of PM emissions by injecting known amounts of liquid fuel onto the piston top using an injector probe. The engine was run predominantly on propane with approximately 10% of the fuel injected as liquid onto the piston. The liquid fuels were chosen to examine the effects of fuel volatility and molecular structure on the PM emissions. A nephelometer was used to characterize the PM emissions. Mass measurements from the nephelometer were compared with gravimetric filter measurements, and particulate size measurements were compared with scanning electron microscope (SEM) photos of particulates captured on filters. The engine was run at 1500 rpm at the Ford world-wide mapping point with an overall equivalence ratio of 0.9.

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.

The effect of the in-cylinder bulk flow on fuel distributions in the cylinder of a motored direct-injection S.I. engine was measured. Five different bulk flows were induced through combinations of shrouded and unshrouded valves, and port deactivation: stock, high tumble, reverse tumble, swirl, and swirl/tumble. Planar Mie scattering was used to observe the fuel spray movement in the centerline plane of a transparent cylinder engine. A fiber optic instrumented spark plug was used to measure the resulting cycle-resolved equivalence ratio in the vicinity of the spark plug. The four-valve engine had the injector located on the cylinder axis; the fiber optic probe was located between the intake valves. Injection timings of 90, 180, and 270 degrees after TDC were examined. Measurements were made at 750 and 1500 rpm with certification gasoline at open throttle conditions. From the images it was found that the type and strength of the bulk flow greatly affected the spray behavior.

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.

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.