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Ongoing efforts in applying a “high-end” turbulent combustion model (a transported probability density function - tPDF - method) to direct-injection internal combustion engines are discussed. New numerical algorithm and physical modeling issues arise compared to more conventional modeling approaches. These include coupling between Eulerian finite-volume methods and Lagrangian Monte Carlo particle methods, liquid fuel spray/tPDF coupling, and heat transfer. Sensitivity studies are performed and quantitative comparisons are made between model results and experimental measurements in a diesel/PCCI engine. Marked differences are found between tPDF results that account explicitly for turbulence/chemistry interactions (TCI) and results obtained using models that do not account for TCI. Computed pressure and heat release profiles agree well with experimental measurements and respond correctly to variations in engine operating conditions.

A study has been experimentally conducted in an optically-accessible DI Diesel engine operating on 50/50 mixture of iso-octane and tetradecane to evaluate a planar laser light scattering technique for the in-cylinder study of soot. Two simultaneous images, taken with vertically and horizontally polarized scattered light, were used to determine the polarization ratio, CHH/CW. This magnitude of the polarization ratio was employed to distinguish soot particles from fuel droplets. The spatial and temporal variations of soot during the combustion cycle were investigated with images taken at various crank angles and swirl levels at three different planes in the combustion bowl. For the high swirl case, soot was uniformly distributed in the combustion bowl. For the non-swirl case, however, soot was mainly observed near the wall and at the top plane, and was observed to exist later into the expansion stroke.

An experimental study was conducted to determine if an organic fuel additive could reduce engine out hydrocarbon and NOx emissions. A production four cylinder spark ignited engine with throttle body fuel injection was used for the study. A full boiling range base fuel, an additized base fuel, a base fuel with methyl tertiary butyl ether (MTBE) and a base fuel with MTBE and additive were used in the engine tests. Additive concentration was 1/2% by mass. Hydrocarbon and NOx measurements were recorded for 11 load/speed conditions. Hydrocarbon speciation data was taken at two of these conditions. The data from the experiments was analyzed in a pair-wise fashion for the fuels with and without the additive to determine whether statistically significant changes occurred.

Several oxygenates have been proposed and tested for use with diesel fuel as a means of reducing exhaust emissions. This paper examines dimethyl ether (DME), which can be produced in many ways including via Air Products and Chemicals, Inc's Liquid Phase Technology (LPDME ™). Modest additions of DME into diesel fuel (2 wt.% oxygen) showed reductions in particulate matter emissions, but the previous data reported by the author from a multicylinder Navistar 7.3L Turbodiesel engine were scattered. In this study, experiments were performed on a multi-cylinder Navistar 7.3L Turbodiesel engine to repeatably confirm and extend the observations from the earlier studies. This is an important step in not only showing that the fuel does perform well in an engine with minor modifications to the fuel system, but also showing that DME can give consistent, significant results in lowering emissions.

Experiments have been conducted in a laminar flow system and in a research engine to investigate the effect of additives on the combustion of gasoline-like fuels. The purpose of the laminar system is to enable rapid screening of additives to determine which, if any, have an enhancing effect on the early stages of combustion, especially under conditions of poor fuel vaporization which exist during cold-start in a spark ignited engine and which make flame propagation difficult to start and sustain. The base fuel used in the laminar and engine systems was a 9 component mixture formulated to simulate those components of gasoline expected to be present in the vapor phase in the intake system of an engine under cold-start conditions. In the laminar system, the pre-mixed, pre-vaporized fuel-air mixture is ignited and a time history of the combustion generated, hydroxyl radical chemiluminescence is recorded.

Results are presented from an experimental study of the effects of engine speed and injection pressure transients on the cold start performance of a gasoline direct injection engine operating on iso-octane. The experiments are performed in an optically-accessible single-cylinder research engine modified for gasoline direct injection operation. In order to isolate the effects of the engine speed and injection pressure transients, three different cold start simulations are used. In the first cold start simulation the engine speed and injection pressure are constant. In the second cold start simulation the injection pressure is constant while the engine speed transient of an actual cold start is simulated. In the third cold start simulation both the engine speed and the injection pressure transients of an actual cold start are simulated.

In this study, performance and emissions characteristics of an LPG direct injection (DI) engine with a rotary distributor pump were examined by using cetane enhanced LPG fuel developed for diesel engines. Results showed that stable engine operation was possible for a wide range of engine loads. Also, engine output power with cetane enhanced LPG was comparable to diesel fuel operation. Exhaust emissions measurements showed NOx and smoke could be reduced with the cetane enhanced LPG fuel. Experimental model vehicle with an in-line plunger pump has received its license plate in June 2000 and started high-speed tests on a test course. It has already been operated more than 15,000 km without any major failure. Another, experimental model vehicle with a rotary distributor pump was developed and received its license plate to operate on public roads.

Biodiesel fuels are widely known to yield an increase in NOx emissions in many diesel engines. It has been suggested that the increase in NOx is due to injection timing differences caused by the low compressibility of biodiesel. In this work, comparisons of injection timing and duration were performed for diesel fuel and a range of biodiesel blends (B20 to B100). The fuel injector on a 4-stroke, single-cylinder, four horsepower, air-cooled, direct injection diesel engine was positioned in a spray chamber while the engine was motored and fuel was delivered to the injector by the fuel pump on the engine. Spray visualization and quantification of injection timing were performed in the spray chamber using an engine videoscope, light attenuation from a HeNe laser and fuel line pressure, and were synchronized to crank shaft position.

In this study, the performance and emissions of a 4 cylinder 2.5L light-duty diesel engine with methane fumigation in the intake air manifold is studied to simulate a dual fuel conversion kit. Because the engine control unit is optimized to work with only the diesel injection into the cylinder, the addition of methane to the intake disrupts this optimization. The energy from the diesel fuel is replaced with that from the methane by holding the engine load and speed constant as methane is added to the intake air. The pilot injection is fixed and the main injection is varied in increments over 12 crank angle degrees at these conditions to determine the timing that reduces each of the emissions while maintaining combustion performance as measured by the brake thermal efficiency. It is shown that with higher substitution the unburned hydrocarbon (UHC) emissions can increase by up to twenty times. The NOx emissions decrease for all engine conditions, up to 53%.

Thermal barrier coated diesel engines, also known as low heat rejection (LHR) engines, have offered the promise of reducing heat rejection to the engine coolant and thereby increasing overall thermal efficiency. However, the larger market potential for thermal barrier coated engines may be in retrofitting in-service diesel engines to reduce particulate emissions. Prior work by the authors has demonstrated a significant decrease in particulate emissions from a thermal barrier coated, single-cylinder, indirect injection (IDI) diesel engine, primarily through reduction of the volatile (VOF) and soluble (SOF) fraction of the particulate. This prior work relied on conventional, commercially available, petroleum-based lubricants. The present study concerns the additional benefits for particulate reduction provided by vegetable oil lubricants. These lubricants are derived from renewable resource materials and can provide a reduction in lubricant generated particulate matter.

This work considers the performance of a NOx control system on a diesel engine and the interaction between the NOx and particulate control devices. A commercial urea-selective catalytic reduction (SCR) catalyst (twin catalytic reactors used in series) was characterized for the impact of nitrogen dioxide (NO2) on the ammonia consumption, production of nitrous oxide (N2O) and relative selectivity of the urea-SCR catalyst for NO2 versus NO when the SCR reactors were positioned downstream of a catalyzed diesel particulate filter (DPF). The aqueous urea solution was injected into the exhaust by using a twin fluid, air-assisted atomizer. It was possible to observe the role of NO2 due to the catalyzed diesel particulate filter (DPF) upstream of the SCR catalyst. This catalyzed DPF oxidizes nitric oxide (NO) in the engine-out emissions to NO2. Further, it uses NO2 to oxidize particulate matter (PM).

A single cylinder engine was operated in HCCI mode with diesel-range fuels, spanning a range in cetane number (CN) from 34 to 62. In addition to measurements of standard gaseous emissions (CO, HC, and NOx), multiple sampling and analysis techniques were used to identify and measure the individual exhaust HC species including an array of oxygenated compounds. A new analytical method, using liquid chromatography (LC) with electrospray ionization-mass spectrometry (ESI-MS) in tandem with ultraviolet (UV) detection, was developed to analyze the longer chain aldehydes as well as carboxylic acids. Results showed an abundance of formic and butyric acid formation at or near the same concentration levels as formaldehyde and other aldehydes.

The gas-phase exhaust emissions which resulted when a variably timed, variable mass of water was injected directly into the cylinder of a spark-ignition engine are reported. The experimental setup and the procedure used in the investigation are also described. Conclusions are drawn with regard to the optimum injection timing and amount of water introduced. Generally, direct-cylinder injection of water reduces NO, increases unburned HC, and does not effect CO and CO2. For a fixed-ignition timing, power also deteriorates. Another finding of this investigation is that direct-cylinder injection does result in NO reductions of better than 85% while using about one-third the mass of water required by manifold injection to effect a similar reduction.

Blends of up to 40% by volume methanol in a methanol-gasoline fuel blend were supplied to a single cylinder engine operating under controlled conditions. The following effects are reported as the methanol concentration increases. The lean misfire limit is extended 0.04 Ø by using a blend containing 40% methanol compared to the base fuel. It is also noted that the lean misfire limit does not vary until a blend containing greater than 20% methanol was used. Torque and thermal efficiency increase significantly. Percent by volume concentrations of carbon monoxide, carbon dioxide and oxides of nitrogen do not change, although oxides of nitrogen reported as mass per power output per hour decrease.

The lean misfire limit air-fuel ratio of a spark ignition engine was extended by various modifications of the intake and ignition systems. The effects of long duration spark, extended spark plug gap projections and gap widths, and a vaned collar intake valve are reported. These modifications allowed for reliable operation up to air-fuel ratios of 24:1. The experimental apparatus and procedure used in this study are described. Conclusions are drawn concerning the optimization of the various modifications to extend the lean misfire limit and reduce the exhaust emissions. In general, all modifications extended the lean misfire limit, but increased gap width had the most profound effect. In all cases, the exhaust emissions were reduced by extension of the lean misfire limit.

A nondimensional representation for a four stroke spark ignition engine was obtained that included the transient charging and exhaust effects. Two basic advantages accrued from this approach; the design and operating parameters that evolved from the nondimensional approach are truly basic in nature, which makes the computer solution more universally applicable to all engines. The inclusion of the transient effects made the representation more realistic and of particular value in the study of engine breathing problems. The effect of valve timing, cam design, valve dimensions, and inlet temperature on engine performance were studied with the computer model.

The cycle-by-cycle variations of the combustion process of a spark ignition engine result in cycle-by-cycle (CBC) variations of the cylinder pressure development histories. Many investigators have postulated that these pressure variations are due to CBC variations of the gas motion near the spark plug at the time of ignition. This investigation was undertaken to determine if such a correlation does in fact exist. The CBC combustion variations of a CFR-RDH engine were examined in terms of the CBC pressure development histories. A constant-temperature hot-film probe was used to determine the velocity variations from cycle to cycle of the motored engine in the vicinity of the spark plug at the crank angles at which ignition would take place under firing conditions. The standard deviations of the gas velocity near the spark plug were correlated to the standard deviations of the crank angle at which maximum pressure occurred for different operating variables.

The ignition of single fuel droplets in air is modeled according to the time-varying conditions within the droplet and the boundary layer around the droplet. Ignition is hypothesized when some point in the boundary layer has experienced a sufficiently severe history in terms of pressure, temperature, equivalence ratio, and time to auto ignite. Experiments were conducted with a wide variety of fuels to validate the model. A critical size concept for ignition was predicted by the model and substantiated by the experiments.

Cycle-to-cycle variations of the combustion process of spark ignition engines, usually observed as peak pressure variations, are a phenomenon whose causes have not yet been identified with certainty. For investigating whether or not there is a relationship between physical cycle characteristics, such as peak pressure, and exhaust gas composition, a sampling system was developed which collects bag samples from specified cycles only. It consists of an analog portion for obtaining pressure and rate-of-pressure change signals, a digital logic portion for discriminating between signals according to selected criteria, and an electrically actuated sampling valve in the engine exhaust system. Since signal analysis and discrimination are instantaneous, gas sampling is done during the exhaust stroke of the same cycle for which the logic generated the command to sample. The system is described in detail and its use is illustrated with an example.

This study shows conclusively that some of the direct microbial mutagenic activity of the soluble-organie-fraction from Diesel particulate matter can be attributed to 1-nitropyrene. 1-nitropyrene has been shown to be formed by the nitration of pyrene, and pyrene is one inherent product of the diffusion-controlled-combustion of hycrocarbons that occurs with Diesel engine operation. Nitrogen dioxide, in the presence of water vapor, is shown to be a potential nitrating agent, and this gas can be produced by the high temperature oxidation of the nitrogen contained in the oxidant. These results are based on studies which used a well-documented engine, model fuel, model oxidants, and synthetic lubricant.