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Homogeneous charge compression ignition offers the potential for significantly lower NOx emissions and up to a 20% improvement in fuel economy relative to a conventional port fuel injected spark ignition (SI) engine. The most significant challenge to developing a production viable HCCI engine is controlling the phasing of autoignition and the combustion rate across the speed and load range of the engine. This report describes an experimental and computational evaluation of controlling HCCI combustion at low loads by adding partial oxidation gas (POx), CO and H2, to the intake manifold. Experiments were performed using charge dilution obtained through conventional exhaust gas recirculation and by modified valve timings to increase the internal residuals. The experimental results showed that POx gas inhibited the low temperature energy release from n-heptane, but promoted the autoignition of isooctane.

A rigidly controlled vehicle test program was conducted to assess the impact of MMT fuel additive on the operation of Low Emission Vehicles (LEVs). Two pairs of each of five vehicle models were tested over extended mileage (75,000 to 100,000 miles). Vehicles were driven on a test track using a customer-type driving cycle and emission tested at regular intervals throughout the program. One vehicle of each pair used a Clear base fuel and the other used the same base fuel with the addition of MMT at a concentration of 8.3 mg Mn/L (0.031 or 1/32 g Mn/US gal). For the four light-duty vehicle models, seven of the eight MMT-fueled vehicles exceeded the NMOG emission certification standards; one Clear-fueled vehicle of one model exceeded the standards, but all other Clear-fueled vehicles met the standards. All four vehicles of the one medium-duty vehicle model met the certification standards, which are higher than those for light-duty vehicles.

The purpose of this research was to investigate the effect of fuel type and mixture composition on hydrocarbon (HC) emissions from a homogeneous charge spark ignition engine. Detailed chemical kinetic modeling indicated that at the temperatures of relevance for HC consumption in engines (T > 1500 K) a majority of the parent fuel decomposes by unimolecular thermal decomposition and that the radical pool which consumes the remaining smaller HC species is produced from the decomposition of the fuel. These results suggested that chemical kinetic interactions should exist between fuel components in a fuel mixture. Engine experiments were performed with iso-octane/toluene and n-octane/toluene fuel mixtures to determine whether kinetic interactions exist within an engine. Engine-out HC emissions exhibited a non-linear response to the amount of the paraffin in the fuel mixture and demonstrated that kinetic interactions do occur between fuel species.

This research investigated the effects of nitric oxide (NO) on hydrocarbon (HC) emissions from a homogeneous charge spark ignition engine. Nitric oxide production inside the engine was eliminated by operating the engine on mixtures of n-butane/O2 and argon mixed from bottled gases in a custom-designed intake system. The effects of NO on HC emissions were studied by adding NO to the intake. No changes in HC emissions were measured with NO addition, although NO addition did promote autoignition chemistry. Experiments were also performed with nitrogen dilution to confirm that the argon results are applicable to normal engine operation. With nitrogen dilution there was again no effect of NO addition on HC emissions. The lack of a chemical effect of NO on HC emissions implies that a majority of the HC consumption occurs at temperatures higher than 1500 K.

The objective of this research was to develop a global correlation for hydrocarbon (HC) emissions from a homogeneous charge spark ignition engine. Engine experiments were performed with a single-cylinder engine over a wide range of speed, load, spark timing and air/fuel ratios using both n-butane and iso-octane for fuels. A global HC consumption rate correlation was developed that was able to predict measured HC emissions from both fuels to within 15 percent over all operating conditions. The results imply that the majority of the HC consumption takes place in the bulk gas at temperatures higher than 1500 K, and that for part load, low speed operating conditions, the majority of the HC consumption takes place within the cylinder before the exhaust valve opens.

Simultaneous tests of emissions and driveability conducted at 4.4°C on a chassis dynamometer using 10 late model vehicles showed a strong correlation between degraded driveability and increased tailpipe hydrocarbon emissions. Other regulated emissions were uncorrelated to driveability, or were small in magnitude. The 24 test gasolines were systematically varied in front-end, mid-range, and tail-end volatility and so spanned much of the moderate and high DI (driveability index) fuel region. Splash blends of 10%.vol ethanol and 15%vol MTBE blended gasolines were tested in addition to hydrocarbon gasolines.

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.

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).

Engine-out and tailpipe exhaust, and hot soak evaporative emissions of two reformulated test gasolines and an Industry Average reference gasoline were compared in four vehicle fleets designed for progressively lower emission standards. The two reformulated gasolines included: 1) a gasoline meeting 1996 California Phase 2 regulatory requirements, and 2) a gasoline blended to the same specifications but without an oxygenated component. These two gasolines were compared with the Auto-Oil Air Quality Improvement Research Program's (AQIRP) Industry Average gasoline representing 1988 national average composition. The vehicle fleets were the AQIRP Older (1983 to 85MY) and Current (1989MY) vehicle fleets used in prior studies, and two new AQIRP test fleets, one designed to 1994 Federal Tier 1 standards and a prototype Advanced Technology fleet designed for lower emission levels of 1995 and later.

Exhaust emissions were measured using a matrix of fuels designed to expand on prior AQIRP work by investigating potential interactive effects of fuel distillation parameters T50 and T90, and of T90 and fuel sulfur content. (T50 and T90 represent the temperature at which 50 or 90% of the fuel distills in a standard test.) This fuel matrix was used also to investigate whether fuel effects found in prior work with then-current vehicle technology can be expected to continue in future lower emission vehicles. An additional pair of fuels was included to extend the range of T50. The vehicles were half of the AQIRP Current fleet (ten vehicles) used in prior studies, and two new fleets of six vehicles each. One of the new fleets was designed to 1994 Federal Tier 1 standards, and the other was Advanced Technology prototypes targeted for lower emission levels of 1995 and later. A set of six fuels was tested in all three fleets.

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.

Exhaust and evaporative emissions from three flexible/variable fuel vehicles (FFV/VFV) were measured as the vehicles operated on E85 fuel (a mixture of 85% ethanol and 15% gasoline) or on gasoline. One vehicle was a production vehicle designed for ethanol fuels and sold in 1992-93 and the other two vehicles were prototypes which were recalibrated 1992 model year methanol FFV's. The gasolines tested were Industry Average Fuel A and a reformulated gasoline Fuel C2 that met California 1996 regulatory requirements. The gasoline component of Fuel E85 was based on the reformulated gasoline. The major findings from this three-vehicle program were that E85 reduced NOx 49% compared to Fuel A and 37% compared to Fuel C2, but increased total toxics 108% (5 mg/mi) and 255% (20 mg/mi), respectively, primarily by increasing acetaldehyde. The NOx effect was significant for both engine-out and tailpipe emissions.

Exhaust and hot soak evaporative emissions were measured in a fleet of 1993 production flexible/variable-fueled vehicles on methanol fuels blended with a reformulated gasoline. A fleet of 1993 California Tier 1 gasoline vehicles was also tested on the same reformulated gasoline blended to meet the specifications of California Phase 2 fuel. Ozone-forming reactivity, expressed as reactivity weighted emissions and specific reactivity, was calculated using 1991 SAPRC and 1994 CBM MIR and MOR factors. Within the FFV/VFV fleet, FTP exhaust and reactivity weighted emissions were significantly lower by 18 to 32% with Phase 2 gasoline relative to Industry Average gasoline. With the exception of greater NMOG emissions with the M85 blends, and lower OMHCE emissions with M85 blended with Industry Average gasoline, exhaust organic emissions, CO and NOx with the methanol fuels were not significantly different than their base gasolines.

Three-day diurnal SHED evaporative emissions were measured in a fleet of ten Auto/Oil current (1989) and 2 older (1984) vehicles using Auto/Oil Industry Average fuel. SHED temperature cycled each 24-hour period from 72 to 96 F (22.2 to 35.5C). Measurements included speciation of individual hydrocarbons in the SHED as well as total mass emissions at the end of each of the three 24-hour test periods. Previous evaporative emission studies provided evidence that permeation and/or fuel seepage could contribute significantly to the mass of diurnal and hot soak emissions. Data from this investigation were used to quantify the contribution of liquid fuel to total SHED emissions during diurnal testing. A calculation method, based on the concentration of 29 select hydrocarbons in the SHED, is presented to apportion SHED emissions between those associated with liquid fuel losses and those associated with fuel tank head space vapor losses.

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.

The analysis of data from the Auto/Oil Air Quality Improvement Research Program (AQIRP) study of the effect of aromatics, MTBE, olefins, and T90 on mass exhaust emissions from current (1989) vehicles was extended to include individual vehicles during individual operating modes. The results of the modal data analysis agree with and complement results which have been reported previously by AQIRP. Beyond this, attention is focused on three fuel compositional changes where the effect on emissions shows a reversal in sign depending on the vehicle operating mode chosen.

Species analyses have been performed on engine-out and tailpipe hydrocarbon mass emissions to help understand why fuels with increasing amounts of heavy hydrocarbon constituents produce significantly higher tailpipe hydrocarbon emissions. Mass and speciated hydrocarbon emissions were acquired for a fleet of ten 1989 model year vehicles operating on twenty-six fuels of differing heavy hydrocarbon composition. These fuels formed two statistically designed matrices: one examining the effects of medium, heavy, and tail reformate and medium and heavy catalytically cracked components; and the other examining the effects of heavy paraffinic versus heavy aromatic components and the effects of the 50% distillation temperature. In this paper the fates of fuel species were traced across the engine and across the catalyst, and correlations were developed between engine-out and tailpipe hydrocarbon species emissions and fuel composition.

Modal analyses have been performed on engine-out and tailpipe hydrocarbon and carbon monoxide mass emissions to help understand why fuels with increasing amounts of heavy hydrocarbon constituents produce significantly higher tailpipe hydrocarbon emissions, yet do not produce significantly higher tailpipe carbon monoxide emissions. Mass emissions were acquired for a fleet of ten 1989 model year vehicles operating on twenty six fuels of differing heavy hydrocarbon composition. These fuels formed two statistically designed matrices: one examining the effects of medium, heavy, and tail reformate and medium and heavy catalytically cracked components; and the other examining the effects of heavy paraffinic versus heavy aromatic components and the effects of the 50% distillation temperature.

Effects of methyl tertiary-butyl ether (MTBE) and tertiary-amyl methyl ether (TAME) on emissions were compared in a fleet of ten 1989 model year vehicles. Test fuels containing 11.5 vol.% MTBE or 12.7 vol.% TAME were blended in a base fuel representing federal emission certification fuel. The oxygen content of both fuels was about 2.0 wt.%. No significant differences were found between the two fuels in exhaust mass HC, NMHC, CO, or NOx; in exhaust or evaporative toxic air pollutants, benzene, 1,3-butadiene, acetaldehyde, or total toxic emissions; or in evaporative hot soak emissions. The only differences found to be significant at the 95% level were in mass and estimated reactivity-weighted diurnal evaporative emissions, for both of which the TAME fuel was about 24% lower than the MTBE fuel; and in formaldehyde emissions, which were 28% higher with the TAME fuel.

Emission effects of gasoline hydrocarbon components distilling above 300°F were investigated to determine whether the effect of 90% distillation temperature (T90) found in an earlier Auto/Oil Program study is due to fuel distillation properties or to hydrocarbon composition, and also to determine whether the T90 effect is linear. Twenty-six fuels were tested in two sets. In Matrix A, the independent variables were catalytically cracked (FCC) and reformate stocks with nominal distillation ranges of 300 to 350, 350 to 400 and 400+°F. In Matrix B, the independent variables were a reformate stock (320 to 370°F), a heavy alkylate (330 to 475°F), and a light alkylate distilling below 300°F, which was used to vary fuel T50 at fixed levels of T90. Exhaust mass and speciation were measured using ten 1989 vehicles of the Auto/Oil Current Fleet. Tailpipe hydrocarbon emissions were found to increase nonlinearly with progressive addition of the heavier components.