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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.

The development of analytic models of diesel engine flow, combustion and subprocesses is described. The models are intended for use as design tools by industry for the prediction of engine performance and emissions to help reduce engine development time and costs. Part of the research program includes performing engine experiments to provide validation data for the models. The experiments are performed on a single-cylinder version of the Caterpillar 3406 engine that is equipped with state-of-the-art high pressure electronic fuel injection and emissions instrumentation. In-cylinder gas velocity and gas temperature measurements have also been made to characterize the flows in the engine.

A constant volume combustion simulation has been used to compute the ignition delays of pure fuels and binary fuel mixtures in air. Minima in the ignition delays were predicted by a comprehensive chemical kinetic mechanism for binary fuel mixtures with methane. A model has been developed to predict the occurrence of autoignition in a spark ignited engine. Experimental pressure data from a CFR engine were used in the model to simulate the temperature-pressure history of the end gas and to determine the time when autoignition occurred. Comprehensive chemical kinetic mechanisms were used to predict the reactions in the end gas. Methanol, methane, ethane, ethylene, propane and n-butane were used as fuels. The initial temperatures in the model were adjusted to give agreement between predicted and observed autoignition. Engine data for methane-ethane mixtures indicated a problem with the kinetic mechanism.

A study was performed in which the effects on the regulated emissions from a commercial small DI diesel engine were measured for different refinery-derived fuel blends. Seven different fuel blends were tested, of which two were deemed to merit more detailed evaluation. To investigate the effects of fuel properties on the combustion processes with these fuel blends, two-color pyrometry was used via optically accessible cylinderheads. Additional data were obtained with one of the fuel blends with a heavy-duty DI diesel engine. California diesel fuel was used as a baseline. The fuel blends were made by mixing the components typically found in gasoline, such as methyl tertiary-butyl ether (MTBE) and whole fluid catalytic cracking gasoline (WH-FCC). The mixing was performed on a volume basis. Cetane improver (CI) was added to maintain the same cetane number (CN) of the fuel blends as that of the baseline fuel.

A single cylinder, Cummins NH, direct-injection, diesel engine has been operated in order to evaluate the effects of aromatic content and aromatic structure on diesel engine particulates. Results from three fuels are shown. The first fuel, a low sulfur Chevron diesel fuel was used as a base fuel for comparison. The other fuels consisted of the base fuel and 10% by volume of 1-2-3-4 tetrahydronaphthalene (tetralin) a single-ring aromatic and naphthalene, a double-ring aromatic. The fuels were chosen to vary aromatic content and structure while minimizing differences in boiling points and cetane number. Measurements included exhaust particulates using a mini-dilution tunnel, exhaust emissions including THC, CO2, NO/NOx, O2, injection timing, two-color radiation, soluble organic fraction, and cylinder pressure. Particulate measurements were found to be sensitive to temperature and flow conditions in the mini-dilution tunnel and exhaust system.

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections.

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.

High bandwidth transient data from a multi-cylinder diesel engine operating in a low temperature combustion regime was analyzed to identify and characterize the transient response behaviors primarily responsible for transient emissions of NO and UHC. Numerous different speed and load transients as well as different combustion modes and control strategies were studied to determine how these parameters affect transient performance. Limitations in the transient response of the air system were found to be the largest contributor to transient emissions, although the mechanism by which these limitations affect performance can vary greatly depending on conditions. Analysis of the data shows that transient emissions for low temperature combustion strategies are highly dependent on cycle-to-cycle changes in intake charge conditions. No fundamental difference was observed between the transient processes controlling speed and load changes.

An analysis of the soot formation and oxidation process in a conventional direct-injection (DI) diesel flame was conducted using numerical simulations. An improved multi-step phenomenological soot model that includes particle inception, particle coagulation, surface growth and oxidation was used to describe the soot formation and oxidation process. The soot model has been implemented into the KIVA-3V code. Other model Improvements include a piston-ring crevice model, a KH/RT spray breakup model, a droplet wall impingement model, a wall-temperature heat transfer model, and the RNG k-ε turbulence model. The Shell model was used to simulate the ignition process, and a laminar-and-turbulent characteristic time combustion model was used for the post-ignition combustion process. Experimental data from a heavy-duty, Cummins N14, research DI diesel engine operated with conventional injection under low-load conditions were selected as a benchmark.

The three-dimensional computer code, KIVA, is being modified to include state-of-the-art submodels for diesel engine flow and combustion. Improved and/or new submodels which have already been implemented are: wall heat transfer with unsteadiness and compressibility, laminar-turbulent characteristic time combustion with unburned HC and Zeldo'vich NOx, and spray/wall impingement with rebounding and sliding drops. Progress on the implementation of improved spray drop drag and drop breakup models, the formulation and testing of a multistep kinetics ignition model and preliminary soot modeling results are described. In addition, the use of a block structured version of KIVA to model the intake flow process is described. A grid generation scheme has been developed for modeling realistic (complex) engine geometries, and initial computations have been made of intake flow in the manifold and combustion chamber of a two-intake-valve engine.

To model sprays from pressure-swirl atomizers, the connection between the injector and the downstream spray must be considered. A new model for pressure-swirl atomizers is presented which assumes little knowledge of the internal details of the injector, but instead uses available observations of external spray characteristics. First, a correlation for the exit velocity at the injector exit is used to define the liquid film thickness. Next, the film must be modeled as it becomes a thin, liquid sheet and breaks up, forming ligaments and droplets. A linearized instability analysis of the breakup of a viscous, liquid sheet is used as part of the spray boundary condition. The spray angle is estimated from spray photographs and patternator data. A mass averaged spray angle is calculated from the patternator data and used in some of the calculations.

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.

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.

More stringent emissions regulations are continually being proposed to mitigate adverse human health and environmental impacts of internal combustion engines. With that in mind, it has been proposed that vehicular particulate matter (PM) emissions should be regulated based on particle number in addition to particle mass. One aspect of this project is to study different sample handling methods for number-based aerosol measurements, specifically, two different methods for removing volatile organic compounds (VOCs). One method is a thermodenuder (TD) and the other is an evaporative chamber/diluter (EvCh). These sample-handling methods have been implemented in an engine test cell with a spark-ignited direct injection (SIDI) engine. The engine was designed for stoichiometric, homogeneous combustion.

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.

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.

Premixed diesel combustion offers the potential of high thermal efficiency and low emissions, however, because the rapid rate of pressure rise and short combustion durations are often associated with low temperature combustion processes, noise is also an issue. The reduction of combustion noise is a technical matter that needs separate attention. Engine noise research has been conducted experimentally with a premixed diesel engine and techniques for engine noise simulation have been developed. The engine employed in the research here is a supercharged, single cylinder DI diesel research engine with a high pressure common rail fuel injection system. In the experiments, the engine was operated at 1600 rpm and 2000 rpm, the engine noise was sampled by two microphones, and the sampled engine noise was averaged and analyzed by an FFT sound analyzer.

In-cylinder measurements of soot particle size, number density, and temperature have been made using optical measurements in a direct injection diesel engine. The measurements were made at one location approximately 5 mm long and 1.5 mm wide above the bowl near the head. Two optical techniques were used simultaneously involving light scattering, extinction and radiation. An optical probe was designed and mounted in a modified exhaust valve which introduced a beam of light into the cylinder and collected the scattered and radiating light from the soot. The resulting measurements were semi-quantitative, giving an absolute uncertainty on the order of ± 50% which was attributed mainly to the uncertainty of the optical properties of the soot and the heterogeneous nature of the soot cloud. Measurements at three speeds and three overall equivalence ratios were made.

The influence of soy- and palm-based biofuels on the in-cylinder sources of unburned hydrocarbons (UHC) and carbon monoxide (CO) was investigated in an optically accessible research engine operating in a partially premixed, low-temperature combustion regime. The biofuels were blended with an emissions certification grade diesel fuel and the soy-based biofuel was also tested neat. Cylinder pressure and emissions of UHC, CO, soot, and NOx were obtained to characterize global fuel effects on combustion and emissions. Planar laser-induced fluorescence was used to capture the spatial distribution of fuel and partial oxidation products within the clearance and bowl volumes of the combustion chamber. In addition, late-cycle (30° and 50° aTDC) semi-quantitative CO distributions were measured above the piston within the clearance volume using a deep-UV LIF technique.

This article presents nondestructive neutron computed tomography (nCT) measurements of Diesel Particulate Filters (DPFs) as a method to measure ash and soot loading in the filters. Uncatalyzed and unwashcoated 200cpsi cordierite DPFs exposed to 100% biodiesel (B100) exhaust and conventional ultra low sulfur 2007 certification diesel (ULSD) exhaust at one speed-load point (1500 rpm, 2.6 bar BMEP) are compared to a brand new (never exposed) filter. Precise structural information about the substrate as well as an attempt to quantify soot and ash loading in the channel of the DPF illustrates the potential strength of the neutron imaging technique.