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The question of whether increasing the fuel economy of light-duty natural gas fueled vehicles can improve their economic competitiveness in the U.S. market, and help the US Department of Energy meet stated goals for such vehicles is explored. Key trade-offs concerning costs, exhaust emissions and other issues are presented for a number of possible advanced engine designs. Projections of fuel economy improvements for a wide range of lean-burn engine technologies have been developed. It appears that compression ignition technologies can give the best potential fuel economy, but are less competitive for light-duty vehicles due to high engine cost. Lean-burn spark ignition technologies are more applicable to light-duty vehicles due to lower overall cost. Meeting Ultra-Low Emission Vehicle standards with efficient lean-burn natural gas engines is a key challenge.

The friction and wear characteristics of three commercially-available, electrolytic coatings for aluminum engine cylinder bores were compared to those of cast iron liners. A Ni/SiC electrocomposite, a hard anodized treatment, and a Plasma Electrolytic Oxidation (PEO) coating were investigated. ASTM standard test method G133-95, non-firing test method, for linearly reciprocating sliding wear was modified to use segments of piston rings and cylinder liners. Tests were conducted using Mr. Goodwrench™ 5W30 as a lubricant at room temperature. The normal force was 150N, the reciprocating frequency was 15Hz, the stroke length was 8mm, and the test duration was 60 minutes. Kinetic friction coefficients ranged from 0.1 to 0.22, typical of boundary lubrication. The Ni/SiC and cast iron samples exhibited the lowest friction. The wear resistance of the Ni/SiC coating was superior to that of cast iron.

Laser-induced incandescence is used to measure time-resolved diesel particulate emissions for two lean NOx trap regeneration strategies that utilize intake throttling and in-cylinder fuel enrichment. The results show that when the main injection event is increased in duration and delayed 13 crank-angle degrees, particulate emissions are very high. For a repetitive pattern of 3 seconds of rich regeneration followed by 27 seconds of NOx-trap loading, we find a monotonic increase in particulate emissions during the loading intervals that approaches twice the initial baseline particulate level after 1000 seconds. In contrast, particulate emissions during the regeneration intervals are constant throughout the test sequence.

Semi-volatile species in the exhaust can condense on the primary particulate matter (PM) forming significant secondary PM mass downstream1. We developed a new thermographic technique to measure the volatility of a particle population. The instrument is called vapor-particle separator (VPS)2. A two-parameter model was used to interpret the thermographic data3. These two parameters define volatilization potential and thermodynamic capacity of the particles. The volatization potential delineates the unique particle volatility, while the thermodynamic capacity illustrates the work required to eliminate the particles. The thermodynamic capacity is found much smaller for small particles than that for large particles.

In this research, small, single cylinder engines have been used to simulate larger engines in the areas of aftertreatment, combustion, and fuel formulation effects. The use of small engines reduces overall research cost and allows more rapid experiments to be run. Because component costs are lower, it is also possible to investigate more variations and to sacrifice components for materials characterization and for subsequent experiments. Using small engines in this way is very successful in some cases. In other cases, limitations of the engines influence the results and need to be accounted for in the experimental design and data analysis. Some of the results achieved or limitations found may be of interest to the small engine market, and this paper is offered as a summary of the authors' research in these areas. Research is being conducted in two areas. First, small engines are being used to study the rapid aging and poisoning of exhaust aftertreatment catalysts.

On a gasoline engine platform, homogeneous charge compression ignition (HCCI) holds the promise of improved fuel economy and greatly reduced engine-out NOx emissions, without an increase in particulate matter emissions. In this investigation, a variable compression ratio (CR) engine equipped with a throttle and intake air heating was used to test the robustness of these control parameters to accommodate a series of fuels blended from reference gasoline, straight run refinery naphtha, and ethanol. Higher compression ratios allowed for operation with higher octane fuels, but operation could not be achieved with the reference gasoline, even at the highest compression ratio. Compression ratio and intake heat could be used separately or together to modulate combustion. A lambda of 2 provided optimum fuel efficiency, even though some throttling was necessary to achieve this condition. Ethanol did not appear to assist combustion, although only two ethanol-containing fuels were evaluated.

A detailed description of a numerical method for computing unsteady flows in engine intake and exhaust systems is given. The calculations include the effects of heat transfer and friction. The inclusion of such calculations in a mathematically simulated engine cycle is discussed and results shown for several systems. In particular, the effects of bell-mouth versus plain pipe terminations and the effects of a finite surge tank are calculated. Experimental data on the effect of heat transfer from the back of the intake valve on wave damping are given and show the effect to be negligible. Experimental data on wave damping during the valve closed period and on the temperature rise of the air near the valve are also given.

The results of both theoretical and experimental studies on the self-ignition of single pure hydrocarbon drops are described. In this work single drops were subjected to air streams heated to such degrees that self-ignition of the drops would occur. Experimental heat and mass transfer parameters, as well as ignition delay data for different fuels and at different operating conditions were obtained. The experimental data were then used in conjunction with boundary layer correlations to evaluate the extent of the ignition delay that is physical (vaporization) and chemical (molecular interaction).

The deactivation of diesel oxidation catalysts (DOCs) by soot contamination and lube-oil derived phosphorus poisoning is investigated. Pt/CeO2/γ-AI2O3 DOCs aged using three different protocols developed by the authors and six high mileage field-returned DOCs of similar formulation are evaluated for THC and CO oxidation performance using a bench-flow reactor. Collectively, these catalysts exhibit a variety of phosphorus and soot morphologies contributing to performance deactivation.

Numerous studies have demonstrated that exhaust gas recirculation (EGR) can attenuate knock propensity in spark ignition (SI) engines at naturally aspirated or lightly boosted conditions [1]. In this study, we investigate the role of cooled EGR under higher load conditions with multiple fuel compositions, where highly retarded combustion phasing typical of modern SI engines was used. It was found that under these conditions, EGR attenuation of knock is greatly reduced, where EGR doesn’t allow significant combustion phasing advance as it does under lighter load conditions. Detailed combustion analysis shows that when EGR is added, the polytropic coefficient increases causing the compressive pressure and temperature to increase. At sufficiently highly boosted conditions, the increase in polytropic coefficient and additional trapped mass from EGR can sufficiently reduce fuel ignition delay to overcome knock attenuation effects.

This paper describes a method for studying reactions of hydrocarbons in S.I. engine exhaust gases. The reaction of ethane is described using an Arrhenius model (experimentally E = 86,500 cal/mole) for the rate of ethane diappearance and empirical correlations for distributions of the products carbon monoxide, ethylene, formaldehyde, methane, acetylene, and propane as a function of the fraction of ethane reacted. The results show that the nature of partial oxidation products from a nonreactive hydrocarbon may be less desirable from an air pollution viewpoint than the initial hydrocarbon.

The ratio of two temperature gradients across the combustion-chamber wall in a diesel engine is used to provide a heat flow ratio showing the radiant heat transfer as a per cent of local total heat transfer. The temperature gradients were obtained with a thermocouple junction on each side of the combustion-chamber wall. The first temperature gradient was obtained by covering the thermocouple at the cylinder gas-wall interface with a thin sapphire window, while the second was obtained without the window. Results show that the time-average radiant heat transfer is of significant magnitude in a diesel engine, and is probably even more significant in heat transfer during combustion and expansion.

Ethanol is a very attractive fuel from an end-use perspective because it has a high chemical octane number and a high latent heat of vaporization. When an engine is optimized to take advantage of these fuel properties, both efficiency and power can be increased through higher compression ratio, direct fuel injection, higher levels of boost, and a reduced need for enrichment to mitigate knock or protect the engine and aftertreatment system from overheating. The ASTM D5798 specification for high level ethanol blends, commonly called “E85,” underwent a major revision in 2011. The minimum ethanol content was revised downward from 68 vol% to 51 vol%, which combined with the use of low octane blending streams such as natural gasoline introduces the possibility of a lower octane “E85” fuel.

The effects of variable compression ratio (CR) and fuel composition on thermal efficiency were investigated in a homogeneous charge compression ignition (HCCI) engine using blends of n-heptane and toluene with research octane numbers (RON) of 0 to 90. Experiments were conducted by performing CR sweeps at multiple intake temperatures using both unthrottled operation, and constant Φ conditions by throttling to compensate for varying air density. It was found that CR is effective at changing and controlling the HCCI combustion phasing midpoint, denoted here as CA 50. Thermal efficiency was a strong function of CA 50, with overly advanced CA 50 leading to efficiency decreases. Increases in CR at a constant CA 50 for a given fuel composition did, in most cases, increase efficiency, but the relationship was weaker than the dependence of efficiency on CA 50.

Engine experiments were conducted on a heavy-duty single-cylinder engine to explore the effects of charge preparation, fuel stratification, and premixed fuel chemistry on the performance and emissions of Reactivity Controlled Compression Ignition (RCCI) combustion. The experiments were conducted at a fixed total fuel energy and engine speed, and charge preparation was varied by adjusting the global equivalence ratio between 0.28 and 0.35 at intake temperatures of 40°C and 60°C. With a premixed injection of isooctane (PRF100), and a single direct-injection of n-heptane (PRF0), fuel stratification was varied with start of injection (SOI) timing. Combustion phasing advanced as SOI was retarded between -140° and -35°, then retarded as injection timing was further retarded, indicating a potential shift in combustion regime. Peak gross efficiency was achieved between -60° and -45° SOI, and NOx emissions increased as SOI was retarded beyond -40°, peaking around -25° SOI.

This study looks at the application of a titanium dioxide (TiO2) catalytic nanoparticle suspension to the surface of the combustion chamber as a coating, as well as the addition of hydrogen gas to a four-stroke spark-ignited carbureted engine as a possible technique for lowering engine-out emissions. The experiments were conducted on two identical Generac gasoline powered generators using two, four and six halogen work lamps to load the engine. One generator was used as a control and the second had key components of the combustion chamber coated with the catalytic suspension. In addition to the coating, both engines were fed a hydrogen and oxygen gas mixture and tested at low, medium and high loads. Using an unmodified engine as a control set, the following three conditions were tested and compared: addition of hydrogen only, addition of coating only, and addition of hydrogen to the coated engine.

The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period.

The objective of this research was to investigate the effect of injection pressure on air entrainment into transient diesel sprays. The main application of interest was the direct injection diesel engine. Particle Image Velocimetry was used to make measurements of the air entrainment velocities into a spray plume as a function of time and space. A hydraulically actuated, electronically controlled unit injector (HEUI) system was used to supply the fuel into a pressurized spray chamber. The gas chamber density was maintained at 27 kg/m3. The injection pressures that were studied in this current research project were 117.6 MPa and 132.3 MPa. For different injection pressures, during the initial two-thirds of the spray plume there was little difference in the velocities normal to the spray surface. For the last third of the spray plume, the normal velocities were 125% higher for the high injection pressure case.

A correlation was developed to predict the ignition delay of PRF blends at a wide range of engine-relevant operating conditions. Constant volume simulations were performed using Cantera coupled with a reduced reaction mechanism at a range of initial temperatures from 570-1860K, initial pressures from 10-100atm, oxygen mole percent from 12.6% to 21%, equivalence ratios from 0.30-1.5, and PRF blends from PRF0 to PRF100. In total, 6,480 independent ignition delay simulations were performed. The correlation utilizes the traditional Arrhenius formulation; with equivalence ratio (φ), pressure (p), and oxygen mole percentage (xo2) dependencies. The exponents α, β, and γ were fitted to a third order polynomial with respect to temperature with an exponential roll-off to a constant value at low temperatures to capture the behavior expressed by the reaction mechanism. The location and rate of the roll-off functions were modified by linear functions of PRF.

Diesel fuels derived from different types of crude oil can exhibit different chemistry while still meeting market requirements and specifications. Oil sands derived fuels typically contain a larger proportion of cycloparaffinic compounds, which result from the cracking and hydrotreating of bitumens in the crude. In the current study, 17 refinery streams consisting of finished fuels and process streams were obtained from a refinery using 100% oil sands derived crude oil. All samples except one met the ULSD standard of 15 ppm sulfur. The samples were characterized for properties and chemistry and run in a simple premixed HCCI engine using intake heating for combustion phasing control. Results indicate that the streams could be equally well characterized by chemistry or properties, and some simple correlations are presented. Cetane number was found to relate mainly to mono-aromatic content and the cycloparaffins did not appear to possess any unique diesel related chemical effects.