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The autoignition chemistries of the olefins 1-butene, 2-butene, isobutene, 2-methyl-2-butene, and 1-hexene and their corresponding paraffins were examined in a motored, single-cylinder engine by measuring stable intermediate species and performing heat-release analyses. The same engine conditions were used for each olefin-paraffin pair, and compression ratio was varied to affect different levels of chemical activity. Paraffin autoignition chemistry is dominated by hydrogen abstraction from the fuel, followed by the intramolecular alkylperoxy isomerization mechanism. Olefin autoignition chemistry differs markedly being controlled by radical addition to the double bond. Hydroxyl radical addition is followed by oxygen addition to the adjacent radical site, followed by scission forming two carbonyls. Hydroperoxyl radical addition yields an epoxy directly. Experimental measurements for each olefin-paraffin pair are compared with each other and with literature values.

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.

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.

Autoignition of the five distinct isomers of hexane is studied experimentally under motored engine conditions and computationally using a detailed chemical kinetic reaction mechanism. Computed and experimental results are compared and used to help understand the chemical factors leading to engine knock in spark-ignited engines and the molecular structure factors contributing to octane rating for hydrocarbon fuels. The kinetic model reproduces observed variations in critical compression ratio with fuel structure, and it also provides intermediate and final product species concentrations in much better agreement with observed results than has been possible previously. In addition, the computed results provide insights into the kinetic origins of fuel octane sensitivity.

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.

Exhaust emissions of three vehicles fueled with compressed natural gas (CNG) were compared with emissions of three counterpart gasoline vehicles. The natural gas vehicles were tested on four CNG fuels covering a wide range of pipeline natural gas compositions. The gasoline vehicles were tested on AQIRP Industry Average gasoline and a reformulated gasoline meeting California 1996 regulatory requirements. Nonmethane hydrocarbon (NMHC) and toxic air pollutant emissions of the CNG vehicles were about one-tenth those of their counterpart gasoline vehicles, while methane emissions were about ten times those of the gasoline vehicles. Carbon monoxide (CO) and nitrogen oxides (NOx) emissions were more variable among the three vehicle pairs. CO emissions ranged from 20 to 80% lower with CNG than with gasoline, and NOx ranged from 80% lower with CNG to equivalent to gasoline.

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.

A reduced autoignition mechanism for iso-octane has been developed by identifying paths to formation of the stable species measured during motoring knock experiments and eliminating paths to formation of species that were not measured. The resulting mechanism includes low-, intermediate-, and high-temperature reactions and consists of 103 species and 131 reactions. This mechanism differs from detailed models not only in the number of reactions and species, but most importantly, in the nature and rates of the degenerate chain branching reactions. To implement this mechanism, a knock subroutine has been added to a quasidimensional spark ignition engine model that accounts for heat losses, blowby, etc. Thus, errors in the reactivity predictions can be assigned almost exclusively to the kinetics. Numerical predictions of the exhaust composition during motoring knock are compared with experimental measurements as a function of compression ratio for several operating conditions.

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.

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 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 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine was tested over the Federal Test Procedure (FTP) driving cycle. Speciated engine-out hydrocarbon emissions were measured. Seven fuels were used for these tests: five blended fuels and two pure hydrocarbon fuels. One of the blended fuels was CARB Phase 2 reformulated gasoline which was used as the reference fuel. The remaining four blended fuels were made from refinery components to meet specified distillation profiles. The pure hydrocarbon fuels were iso-octane and toluene - an alkane and an aromatic with essentially identical boiling points. The five blended fuels can be grouped to examine the effects of fuel volatility and MTBE. Additionally, correlations were sought between the fuel properties and the Specific Reactivity, the exhaust “toxics”, and the pass-through of unburned fuel species.

The effect of gasoline olefin composition and content on urban ozone was estimated using the Urban Airshed Model (UAM), emission measurements for a base fuel, and projected emissions for two hypothetical fuels with reduced olefin content. The projected emissions for the hypothetical fuels were developed using regressions developed from Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase I testing, a vapor headspace model and other information. Ozone modeling was conducted for Los Angeles in year 2010 and Dallas-Fort Worth and New York in year 2005. When all olefins were removed from the base fuel, the light-duty vehicle contribution to peak hourly ozone was reduced by 8 to 12%. This corresponds to a projected reduction of 0.6 to 0.8% in total peak ozone from all sources. Removing only light (C5) olefins provided 67 to 78% of the peak ozone benefit from removal of all olefins.

In this pilot study conducted by the Auto/Oil Air Quality Improvement Research Program, engine-out and tailpipe speciated hydrocarbon emissions were obtained for three vehicles operated over the Federal Test Procedure on two different fuels, both of which were speciated. The fates of the fuel species were traced across the engine and across the catalyst, and relationships were developed between engine-out and tailpipe hydrocarbon emissions and fuel composition. These relationships allowed separating the fuel's contribution to engine-out and tailpipe hydrocarbon emissions into two parts, unreacted fuel and partial oxidation products. Specific ozone reactivities and toxic air pollutants were analyzed for both engine-out and tailpipe emissions. Vehicle-to-vehicle, fuel-to-fuel, and bag-to-bag differences have been highlighted.

Modal analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with higher T50 and/or T90 distillation temperatures produce somewhat higher engine-out hydrocarbon emissions and substantially higher tailpipe hydrocarbon emissions. Modal analyses were also performed to examine how increased fuel sulfur increases tailpipe hydrocarbon emissions and to identify which gasoline properties in this study are responsible for the lower tailpipe hydrocarbon emissions with reformulated gasolines. These analyses were performed on three different test vehicle fleets representing varying levels of emissions control technology. The modal analyses showed that the substantially higher tailpipe hydrocarbon emissions from fuels with high T50 and/or T90 distillation temperatures result primarily from these fuels producing substantially higher engine-out hydrocarbon emissions during the first cycle of the Federal Test Procedure (FTP).

Species analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with higher T50 and/or T90 distillation temperatures produce higher engine-out and tailpipe hydrocarbon emissions and why fuels with higher T90 distillation temperatures produce higher engine-out and tailpipe specific reactivities. Species analyses were also performed to examine the effects of fuel sulfur level on engine-out and tailpipe species and specific reactivities. These analyses were performed on three different test-vehicle fleets representing varying levels of emissions control technology and the effect of emissions control technology was examined. Individual hydrocarbon species concentrations in both the engine-out and tailpipe were found to correlate linearly with the concentrations of the same species in the fuel, implying that a small fraction of the fuel escapes the combustion process and conversion over the catalyst.

Effects of gasoline sulfur content on emissions were measured in a fleet of ten 1989 model year vehicles. Two ranges of sulfur content were examined. In a set of five fuels, reducing sulfur from 450 to 50 ppm, reduced fleet average tailpipe emissions of HC, NMHC and CO each by about 18%, and reduced NOx 8%. The largest effect on HC and CO emissions was observed in FTP Bag 2. This and the absence of any significant effect on engine emissions indicate that sulfur affected the performance of the catalytic converters. The response of HC and NMHC to fuel sulfur content was non-linear and increased as sulfur level was reduced. In the second set of three fuels, reducing sulfur from 50 to 10 ppm reduced HC and NMHC by 6% and CO by 10%, but had no significant effect on NOx. The effects on HC, NMHC and NOx were not significantly different from predictions based on the prior fuel set. The reduction in CO was larger than predicted.