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The objective of this research is a detailed investigation of particulate sizing and number count from a spark-ignited, direct-injection (SIDI) engine at different operating conditions. The engine is a 549 [cc] single-cylinder, four-valve engine with a flat-top piston, fueled by Tier II EEE. A baseline engine operating condition, with a low number of particulates, was established and repeatability at this condition was ascertained. This baseline condition is specified as 2000 rpm, 320 kPa IMEP, 280 [°bTDC] end of injection (EOI), and 25 [°bTDC] ignition timing. The particle size distributions were recorded for particle sizes between 7 and 289 [nm]. The baseline particle size distribution was relatively flat, around 1E6 [dN/dlogDp], for particle diameters between 7 and 100 [nm], before dropping off to decreasing numbers at larger diameters. Distributions resulting from a matrix of different engine conditions were recorded.

Diesel particulate samples were collected from a light duty engine operated at a single speed-load point with a range of biodiesel and conventional fuel blends. The oxidation reactivity of the samples was characterized in a laboratory reactor, and BET surface area measurements were made at several points during oxidation of the fixed carbon component of both types of particulate. The fixed carbon component of biodiesel particulate has a significantly higher surface area for the initial stages of oxidation, but the surface areas for the two particulates become similar as fixed carbon oxidation proceeds beyond 40%. When fixed carbon oxidation rates are normalized to total surface area, it is possible to describe the oxidation rates of the fixed carbon portion of both types of particulates with a single set of Arrhenius parameters. The measured surface area evolution during particle oxidation was found to be inconsistent with shrinking sphere oxidation.

Sources of unburned hydrocarbon (UHC) emissions are examined for a highly dilute (10% oxygen concentration), moderately boosted (1.5 bar), low load (3.0 bar IMEP) operating condition in a single-cylinder, light-duty, optically accessible diesel engine undergoing partially-premixed low-temperature combustion (LTC). The evolution of the in-cylinder spatial distribution of UHC is observed throughout the combustion event through measurement of liquid fuel distributions via elastic light scattering, vapor and liquid fuel distributions via laser-induced fluorescence, and velocity fields via particle image velocimetry (PIV). The measurements are complemented by and contrasted with the predictions of multi-dimensional simulations employing a realistic, though reduced, chemical mechanism to describe the combustion process.

The objective of this research is a detailed investigation of multiple injections in a highly-dilute diesel low temperature combustion (LTC) regime. This research concentrates on understanding the performance and emissions benefits of multiple injections via experiments and simulations in a 0.48L signal cylinder light-duty engine operating at 2000 r/min and 5.5 bar IMEP. Controlled experiments in the single-cylinder engine are then combined with three computational tools, namely heat release analysis of measured cylinder pressure, a phenomenological spray model using in-cylinder thermodynamics [1], and KIVA-3V Chemkin CFD computations recently tested at LTC conditions [2]. This study examines the effects of fuel split distribution, injection event timing, rail pressure, and boost pressure which are each explored within a defined operation range in LTC.

This paper investigates flow and combustion in a full-cycle simulation of a four-stroke, three-valve HCCI engine by visualizing the flow with pathlines. Pathlines trace massless particles in a transient flow field. In addition to visualization, pathlines are used here to trace the history, or evolution, of flow fields and species. In this study evolution is followed from the intake port through combustion. Pathline analysis follows packets of intake charge in time and space from induction through combustion. The local scalar fields traversed by the individual packets in terms of velocity magnitude, turbulence, species concentration and temperatures are extracted from the simulation results. The results show how the intake event establishes local chemical and thermal environments in-cylinder and how the species respond (chemically react) to the local field.

An investigation of the effect of microflow machining on the spray characteristics of diesel injectors was undertaken. A collection of four VCO injector tips were tested prior to and after an abrasive flow process using a high viscosity media. The injector nozzles were tested on a spray fixture. Rate of injection measurements and high-speed digital images were used for the quantification of the air entrainment rate. Comparisons of the spray characteristics and A/F ratios were made for conditions of before and after the abrasive flow process. Results showed a significant decrease in the injection-to-injection variability and improvement of the spray symmetry. A link between the quantity of air entrained and potential differences in spray plume internal chemical composition and temperature is proposed via equilibrium calculations.

Multi-dimensional computational efforts using comprehensive and skeletal kinetics have been made to investigate the cool flame region in HCCI combustion. The work was done in parallel to an experimental study that showed the impact of the negative temperature coefficient and the cool flame on the start of combustion using different fuels, which is now the focus of the simulation work. Experiments in a single cylinder CFR research engine with n-butane and a primary reference fuel with an octane number of 70 (PRF 70) were modeled. A comparison of the pressure and heat release traces of the experimental and computational results shows the difficulties in predicting the heat release in the cool flame region. The behavior of the driving radicals for two-stage ignition is studied and is compared to the behavior for a single-ignition from the literature. Model results show that PRF 70 exhibits more pronounced cool flame heat release than n-butane.

An experimental study was performed to investigate the effect of fuel composition on combustion, gaseous emissions, and detailed chemical composition and size distributions of diesel particulate matter (PM) in a modern heavy-duty diesel engine with the use of the enhanced full-dilution tunnel system of the Engine Research Center (ERC) of the UW-Madison. Detailed description of this system can be found in our previous reports [1,2]. The experiments were carried out on a single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system. The operating conditions of the engine followed the California Air Resources Board (CARB) 8-mode test cycle. The fuels used in the current study include baseline No. 2 diesel (Fuel A: sulfur content = 352 ppm), ultra low sulfur diesel (Fuel B: sulfur content = 14 ppm), and Fisher-Tropsch (F-T) diesel (sulfur content = 0 ppm).

An experimental study was carried out to investigate the effects of fuel injection timing on detailed chemical composition and size distributions of diesel particulate matter (PM) and regulated gaseous emissions in a modern heavy-duty D.I. diesel engine. These measurements were made for two different diesel fuels: No. 2 diesel (Fuel A) and ultra low sulfur diesel (Fuel B). A single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system was used in the experiments. PM measurements were made with an enhanced full-dilution tunnel system at the Engine Research Center (ERC) of the University of Wisconsin-Madison (UW-Madison) [1, 2]. The engine was run under 2 selected modes (25% and 75% loads at 1200 rpm) of the California Air Resources Board (CARB) 8-mode test cycle.

Current regulations stipulate acceptable levels of particulate emissions based on the mass collected on filters obtained by sampling in diluted exhaust. Although precise, this gives us only aggregated information. If in addition to the mass based measurements, detailed chemical analysis of the particulate matter (PM) is performed, additional subtle information about the combustion process can be revealed. This paper reports the results of detailed chemical analysis of trace metal in the PM emitted from a single cylinder heavy-duty diesel engine. The trace metal concentrations are used as an indicator of oil consumption. Two techniques were used to make the trace metal concentration measurements. PM was captured on filters and trace metals were quantified with an Inductively Coupled Plasma Mass Spectrometer (ICPMS), and also an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to perform particle size and composition measurements in real time.

A single cylinder CFR research engine has been run in HCCI combustion mode for a range of temperatures and fuel compositions. The data indicate that the best HCCI operation, as measured by a combination of successful combustion with low ISFC, occurs at or near the rich limit of operation. Analysis of the pressure and heat release histories indicated the presence, or absence, and impact of the fuel's NTC ignition behavior on establishing successful HCCI operation. The auto-ignition trends observed were in complete agreement with previous results found in the literature. Furthermore, analysis of the importance of the fuel's octane sensitivity, through assessment of an octane index, successfully explained the changes in the fuels auto-ignition tendency with changes in engine operating conditions.

A series of engine experiments have been performed to explore the impact intake temperature, engine speed and fuel composition on the HCCI operating range of a CFR engine. The experimental matrix covers a range of engine speeds 600 - 2000 RPM), intake temperatures (300 K - 400 K), and four different fuels. Three of the fuels had different chemical composition but had equivalent research octane numbers of 91.8. The fourth fuel, a blend of primary reference fuels had a research octane number of 70. The acceptable HCCI operating range of the engine was defined through two criteria; the rate of pressure rise needed to be less than 10 MPa per crank angle and the covariance of the indicated mean effective pressure needed to be less than 10 percent. Using these limits the HCCI operating range for the engine was evaluated for the experimental matrix. Data for emissions, and fuel consumption as well as in-cylinder pressure were recorded.

An investigation of several diesel injector nozzles that produced different engine emissions performance was performed. The nozzle styles used were two VCO type nozzles that were manufactured using two different techniques, and two mini-sac nozzles that provided comparison. Fired experiments were conducted on a Detroit Diesel Series 50 engine. Optical access was obtained by substituting a sapphire window for one exhaust valve. Under high speed, high load, retarded injection timing conditions, it was discovered that each nozzle produced different specific soot and NOx emissions. High-speed film images were obtained. It was discovered that the temperature and KL factor results from the 2-color optical pyrometry showed significant differences between the nozzles. The authors propose the possibility that differences in air entrainment, caused by potential differences in CD due to surface finish, may contribute to the variance in emissions performance.

An engine cycle simulation code with detailed chemical kinetics has been developed to study Homogeneous Charge Compression Ignition (HCCI) combustion with hydrogen as the fuel. In order to attain adequate combustion duration, resulting from the self-accelerating nature of the chemical reaction, fuel and temperature inhomogeneities have been brought to the calculation by considering the combustion chamber to have various temperature and fuel distributions. Calculations have been done under various conditions including both perfectly homogeneous and inhomogeneous cases, changing the degree of inhomogeneity. The results show that intake gas temperature is more dominant on ignition timing of HCCI than equivalence ratio and that there is a possibility to control HCCI by introducing appropriate temperature inhomogeneity to in-cylinder mixture.

The authors used auxiliary gas injection (AGI) to increase in-cylinder mixing during the latter portion of combustion in a direct injection (DI) diesel engine in order to reduce soot emissions without affecting NOx. Experiments were conducted using various gas injection directions and compositions to explore the effect of these parameters. Simulations were employed to provide additional insight. AGI direction was found to have a profound impact on soot emissions. Researchers suggested that this was due to changes in the fuel spray-gas jet interaction with injection direction. Simulations supported this theory and suggested that the number of soot clouds affected by the gas jet may also be a factor. The oxygen content of the gas jet was also found to have an influence on emissions. Researchers found that, when the oxygen content of the gas jet was increased, soot emissions decreased. However, this was found to have a detrimental affect on NO.

Oxygen enhancement in a direct injection (DI) diesel engine was studied to investigate the potential for particulate matter and NOx emissions control. The local oxygen concentration within the fuel plume was modified by oxygen enrichment of the intake air and by oxygenating the base fuel with 20% methyl t-butyl ether (MTBE). The study collected overall engine performance and engine-out emissions data as well as in-cylinder two-color measurements at 25% and 75% loads over a range of injection timings. The study found oxygen enhancement, whether it be from intake air enrichment or via oxygenated fuels, reduces particulate matter, the effectiveness depending on the local concentration of oxygen in the fuel plume. Since NOx emissions depend strongly on the temperature and oxygen concentration throughout the bulk cylinder gas, the global thermal and dilution effects from oxygen enrichment were greater than that from operation on oxygenated fuel.

This paper will focus on the spray characteristics of a high pressure (up to 155 MPa) accumulator type injector in a high pressure (chosen density) quiescent spray chamber. The injector uses a standard single orifice nozzle which produces a full cone spray. Using this apparatus, we are examining the fundamental aspects of high pressure spray formation under controlled conditions. Experimental data was collected using high speed photography (10,000 frames per second) which used a pulsed copper-vapor laser as a light source. Two photographic techniques are being utilized. Direct attenuation allows measurement of tip penetration, spray cone angle, and injection duration. Scattering from a sheet of laser light perpendicular to the camera field of view is being developed in an attempt to resolve inner spray cone structure. In addition to the quantitative data from the high speed photography, injector accumulator pressure, supply pressure and injection rate histories were recorded.

Laser Doppler velocimetry has been used to measure velocity and turbulence intensity profiles in the wall boundary layer of a spark-ignited homogeneous-charge research engine. By using a toroidal contoured engine head it was possible to bring the laser probe volume to within 60 μm of the wall. Two different levels of engine swirl were used to vary the flow Reynolds number. For the high swirl case under motored operation the boundary layer thickness was less than 200 μm, and the turbulence intensity increased as the wall was approached. With low swirl the 700-1000 μm thick boundary layer had a velocity profile that was nearly laminar in shape, and there was no increase in turbulence intensity near the wall. When the engine was fired the boundary layer thickness increased for both levels of swirl.

A model developed to predict outoignition is used with data from a premixed charge, spark-ignition engine. A detailed chemical kinetics mechanism is used to predict the reactions which occur in the end-gas and lead to autoignition. Experimental pressure data from a CFR engine are used in the model to determine end-gas temperatures. The initial temperature at the time of spark must be increased above the bulk temperature for the predicted time of outoignition to agree with the observed time. A method for estimating the initial temperature based on an adiabotic compression from the time of intake valve closing is presented. The predictions of the model are examined over a range of engine speeds and fuel-air equivalence ratios. The magnitude by which the initial temperature must be increased above the bulk temperature decreases with increasing engine speed. This magnitude follows a trend which can be related to a heat transfer correlation.

The heat release type models have been classified as zero-dimensional because they have no spatial resolution and therefore don't contain any information on the fluid mechanics in them. They have been a significant contribution because they incorporate the rate processes occurring in the engine and are an aid in the analysis of the data. Because they are thermodynamic models it is necessary to define the control volumes on which the thermodynamic analysis is to be performed. The different control volume descriptions, called one, two and three zone models, and the analysis of the combustion event using these models is discussed. Finally a description of second law zero-dimensional models is given. These models have similar limitations as the First Law models; no spatial resolution and a control volume definition is required. These models are useful because they enable one to analyze the magnitude of the losses that occur in the different processes which comprise the engine cycle.