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A single-cylinder, spark-ignited engine was run on a certification test gasoline to saturate the oil in the sump with fuel through exposure to blow-by gas. The sump volume was large relative to production engines making its absorption-desorption time constant long relative to the experimental time. The engine was motored at 1500 RPM, 90° C coolant and oil temperature, and 0.43 bar MAP without fuel flow. Exhaust HC concentrations were measured by on-line FID and GC analysis. The total motoring HC emissions were 150 ppmC1; the HC species distribution was heavily weighted to the low-volatility components in the gasoline. No high volatility components were visible. The engine was then fired on isooctane fuel at the above conditions, producing a total engine-out HC emission of 2300 ppmC1 for Φ = 1.0 and MBT spark timing.

Fuel-air mixing in a direct-injection SI engine was studied to further improve full-load torque output. The fuel-injection location of DI vs. PFI results in different heat sources for fuel evaporation, hence a DI engine has been found to exhibit higher volumetric efficiency and lower knocking tendency, resulting in higher full-load torque output [1]. The ability to change injection timing of the DI engine affects heat transfer and mixture temperature, hence later injection results in lower knocking tendency. Both the higher volumetric efficiency and the lower knocking tendency can improve engine torque output. Improving volumetric efficiency requires that the fuel is injected during the intake stroke. Reducing knocking tendency, in contrast, requires that the fuel is injected late during the compression stroke. Thus, a strategy of split injection was proposed to compromise the two competing requirements and further increase direct-injection SI engine torque output.

The fiber optic spark plug was used in conjunction with a piezoelectric pressure transducer to collect combustion diagnostic data on four production engines designed to generate quiescent, swirl, and tumble charge motions. Spark advance was varied under low speed, low load conditions to investigate changes in flame kernel behavior and in-cylinder charge motion as functions of crank angle and spark advance. Two flame kernel models were filled to the data and a critical comparison of the models was conducted. Flame kernel behavior was represented by three values: convection velocity, growth rate, and convection direction. Convection velocity was highest in the swirl chambers. It also varied considerably among cylinders in the same engine. Growth rate correlated well with 0-2% burn but showed negligible correlations with later burn or IMEP. Convection direction proved useful in determining flow direction near the plug.

Current demands for high fuel efficiency and low emissions in automotive powerplants have drawn attention to the two-stroke engine configuration. The present study measured trapping and scavenging efficiencies of a firing two-stroke spark-ignition engine by in-cylinder gas composition analysis. Intermediate results of the procedure included the trapped air-fuel ratio and residual exhaust gas fraction. Samples, acquired with a fast-acting electromagnetic valve installed in the cylinder head, were taken of the unburned mixture without fuel injection and of the burned gases prior to exhaust port opening, at engine speeds of 1000 to 3000 rpm and at 10 to 100% of full load. A semi-empirical, zero-dimensional scavenging model was developed based on modification of the non-isothermal, perfect-mixing model. Comparison to the experimental data shows good agreement.

For several years, a single-cylinder, spark-ignited engine without catalyst has been operated at Ford on single-component fuels that are constituents of gasoline as well as on simple fuel mixtures. This paper presents a review of these experiments as well as others pertinent to understanding hydrocarbon emissions. The engine was run at four steady-state conditions which are typical of normal operation. The fuel structure and the engine operating conditions affected both the total HC emissions and the reactivity of these emissions for forming photochemical smog in the atmosphere. These experiments identified major precursor species of the toxic HC emissions benzene and 1,3-butadiene to be alkylated benzenes and either straight chain terminal olefins or cyclic alkanes, respectively. In new data presented, the primary exhaust hydrocarbon species from MTBE combustion is identified as isobutene.

A hydrocarbon trapping system for cold start emissions was constructed and tested using two types of carbonaceous adsorbents provided by Corning, Inc. One was made by combining activated carbon with an organic binder and extruding it into a honeycomb, and the other by depositing a carbon coating on a ceramic monolith. The tests were carried out on an engine in a dynamometer laboratory to characterize the performance of the carbon elements under transient cold start conditions. Performance was evaluated by continuously measuring exhaust gas hydrocarbon concentrations upstream and downstream of the trap, using conventional emissions consoles. Samples were also collected for off-line analysis of individual hydrocarbon species using gas chromatography to examine differences in adsorption of individual species. The speciated hydrocarbon data were used to distinguish between the mass trapping efficiency and a reactivity-based trapping efficiency of the adsorbant traps.

Modern four-valve engines are running at ever higher compression ratios in order to improve fuel efficiency. Hotter cylinder bores also can produce increased fuel economy by decreasing friction due to less viscous oil layers. In this study changes in compression ratio and coolant temperature were investigated to quantify their effect on exhaust emissions. Tests were run on a single cylinder research engine with a port-deactivated 4-valve combustion chamber. Two compression ratios (9.15:1 and 10.0:1) were studied at three air/fuel ratios (12.5, 14.6 and 16.5) at a part load condition (1500 rpm, 3.8 bar IMEP). The effect of coolant temperature (66 °C and 108°C) was studied at the higher compression ratio. The exhaust was sampled and analyzed for both total and speciated hydrocarbons. The speciation analysis provided concentration data for hydrocarbons present in the exhaust containing twelve or fewer carbon atoms.

As vehicle tailpipe emission levels decrease with improvements in emission control technology and reformulation of gasolines, exhaust hydrocarbon levels begin to approach the levels in ambient air. Hydrocarbon speciation at these low levels requires high sensitivity capillary gas chromatography methods. In this study, a mixture of “synthetic” exhaust was prepared at two concentration levels (approximately 5 ppm C and 10 ppm C), and was analyzed by the widely-used Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase II (gas chromatography) speciation method with a sensitivity of 0.005 ppm C for individual species. The mixture at each concentration level, along with a sample of ambient air, was analyzed a total of 20 times on 10 separate days over a 2½ week period. Concentrations of total hydrocarbons (HCs) and individual species (using the AQIRP library) were measured; averages and standard deviations were calculated.

Although much has been learned in recent years about the atmospheric reactivity of the hydrocarbon (HC) emissions from gasoline-fueled vehicles, there is only a limited database of corresponding information for exhaust emissions from diesel-fueled vehicles. An assessment of exhaust reactivity requires “speciation”, or measurement of the individual species of the HC fraction. The HC exhaust emissions are a complex mixture of unburned and partially burned fuel components. Because diesel fuel contains a much higher molecular weight range (typically C9-C26) than gasoline (typically C5-C12), new methodology was required to accommodate the collection and analysis of the >C12 fraction of the HC exhaust. As part of a study of the effects of fuel and other factors on the chemical nature of diesel emissions, we have developed a method for the collection and analysis of the semivolatile or heavy HC (>C12) fraction of the exhaust.

Total and speciated, engine-out, hydrocarbon (HC) emissions have been measured as a function of time after a 23°C cold start of a gasoline-fueled, V-8 engine. Hydrocarbon emissions from two fuel injection systems were compared: a production port-fuel-injection (PFI) system; and a pre-vaporized (heated) central-fuel-injection (PV-CFI) system. The results indicate that, for this particular engine at the chosen operating conditions, the effect of fuel preparation on HC emissions during cold start is minimal at low load (2.57 bar IMEP (gross), MAP = 0.34 bar) but becomes significant at higher load (5.15 bar IMEP, MAP = 0.58 bar) early in the cold start. Comparison of the relative contribution to the exhaust HC of a series of fuel-derived alkanes suggests that fuel absorption in oil films is a minor contributor to HC emissions from this engine during a 23°C cold start.

Multidimensional modeling is used to study air-fuel mixing in a direct-injection spark-ignition engine. Emphasis is placed on the effects of the start of fuel injection on gas/spray interactions, wall wetting, fuel vaporization rate and air-fuel ratio distributions in this paper. It was found that the in-cylinder gas/spray interactions vary with fuel injection timing which directly impacts spray characteristics such as tip penetration and spray/wall impingement and air-fuel mixing. It was also found that, compared with a non-spray case, the mixture temperature at the end of the compression stroke decreases substantially in spray cases due to in-cylinder fuel vaporization. The computed trapped-mass and total heat-gain from the cylinder walls during the induction and compression processes were also shown to be increased in spray cases.

The new California LEV-II regulations for “near zero” evaporative emissions require a 75% reduction from current emission levels for light duty vehicles. To meet the challenge of satisfying these new regulations, there is an immediate need for an increased understanding of the sources of evaporative emissions. Hydrocarbon speciation by gas chromatography is a powerful analytical tool for determining the composition of complex hydrocarbon mixtures. Gas chromatography and gas chromatography/mass spectrometry were used to identify the volatile organic compounds (VOC) present in the evaporative emissions from a number of prototype and recent production model gasoline-fueled vehicles. For a “typical” evaporative emissions sample, more than 90% of the emissions were found to be fuel-type hydrocarbons.

A small-bore 4-stroke single-cylinder stratified-charge DISI engine using an air-forced fuel injection system has been designed and tested under various operating conditions. At light loads, fuel consumption was improved by 16∼19% during lean, stratified-charge operation at an air-fuel ratio of 37. NOx emissions, however, were tripled. Using EGR during lean, stratified-charge operation significantly reduced NOx emissions while fuel consumption was as low as the best case without EGR. It was also found that combustion and emissions near the lean limit were a strong function of the combination of injection and spark timings, which affect the mixing process. Injection pressure, air injection duration, and time delay between fuel and air injections also played a role. Generating in-cylinder air swirl motion slightly improved fuel economy.

The effects of fuel injection and spark timing on engine-out, regulated (total HC, NOx, and CO) and speciated HC emissions have been investigated for a 0.31L, single-cylinder, direct-injection, spark-ignition (DISI) engine equipped with an air-forced fuel injector. When the timing of the start of the air injection (SOA) is varied during high stratification operation, the mole fractions of all regulated emissions vary sharply over relatively small (20-30 crank angle degrees) changes in SOA. In addition, the distribution of exhaust hydrocarbon species changes significantly. As stratification increases, the contribution of unburned paraffinic fuel components to the HC emissions decreases by a factor of two while the olefinic partial oxidation products increase. When the spark timing is varied during high stratification operation, the HC emissions increase sharply as the spark timing is retarded relative to MBT.

Although the intent of the SHED test (Sealed Housing for Evaporative Determination) is to measure evaporative fuel losses, the SHED sampling methodology in fact measures hydrocarbons from all vehicle and test equipment sources. Leakage of air conditioning (AC) refrigerant is one possible non-fuel source contributing to the SHED hydrocarbon measurement. This report describes a quick and relatively simple method to identify the contribution of AC refrigerant to the SHED analyzer reading. R134A (CH2FCF3), the hydrofluorocarbon refrigerant used in all current automotive AC systems, as well as its predecessor, the chlorofluorocarbon R12, can be detected using the gas chromatography methods currently in place at many emissions labs for the speciation of exhaust and evaporative hydrocarbon emissions.

Analytical procedures for the speciation of hydrocarbons and oxygenates (ethers, aldehydes, ketones and alcohols) in vehicle evaporative and tailpipe exhaust emissions have been improved for Phase II studies of the Auto/Oil Air Quality Improvement Research Program (AQIRP). One gas chromatograph (GC) was used for measurement of C1-C4 species and a second GC for C4-C12 species. Detection limits for this technique are 0.005 ppm C or 0.1 mg/mile exhaust emission level at a chromatographic signal-to-noise ratio of 3/1, a ten-fold improvement over the Phase I technique. The Phase I library was modified to include additional species for a total of 154 species. A 23-component gas standard was used to establish a calibration scale for automated computer identification of species. This method identifies 95±3% of the total hydrocarbon mass measured by GC for a typical exhaust sample. Solid adsorbent cartridges or impingers were used to collect aldehydes and ketones.

An analytical method for the determination of hydrocarbon and ether emissions from gasoline-, methanol-, and flexible-fueled vehicles is described. This method was used in Phase I of the Auto/Oil Air Quality Improvement Research Program to provide emissions data for various vehicles using individual reformulated gasolines and alternate fuels. These data would then be used for air modeling studies. Emission samples for tailpipe, evaporative, and running loss were collected in Tedlar bags. Gas chromatographic analysis of the emissions samples included 140 components (hydrocarbons, ethers, alcohols and aldehydes) between C1 and C12 in a single analysis of 54-minutes duration. Standardization, quality control procedures, and inter-laboratory comparisons developed and completed as part of this program are also described.

Speciated HC emissions from the exhaust system of a production engine without an active catalyst have been obtained with 3 sec time resolution during a 70°F cold start using two control strategies. For the conventional cold start, the emissions were initially enriched in light fuel alkanes and depleted in heavy aromatic species. The light alkanes fell rapidly while the lower vapor pressure aromatics increased over a period of 50 sec. These results indicate early retention of low vapor pressure fuel components in the intake manifold and exhaust system. Loss of higher molecular weight HC species does occur in the exhaust system as shown by experiments in which the exhaust system was preheated to 100° C. The atmospheric reactivity of the exhaust HC emissions for photochemical smog formation increases as the engine warms.