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We have developed a methodology for predicting combustion and emissions in a Homogeneous Charge Compression Ignition (HCCI) Engine. The methodology judiciously uses a fluid mechanics code followed by a chemical kinetics code to achieve great reduction in the computational requirements; to a level that can be handled with current computers. In previous papers, our sequential, multi-zone methodology has been applied to HCCI combustion of short-chain hydrocarbons (natural gas and propane). Applying the same procedure to long-chain hydrocarbons (iso-octane) results in unacceptably long computational time. In this paper, we show how the computational time can be made acceptable by developing a segregated solver. This reduces the run time of a ten-zone problem by an order of magnitude and thus makes it much more practical to make combustion studies of long-chain hydrocarbons.

We have developed a model of the diesel fuel injection process for application to analysis of low temperature non-sooting combustion. The model uses a simplified mixing correlation and detailed chemical kinetics to analyze a parcel of fuel as it moves along the fuel jet, from injection to evaporation and ignition. The model predicts chemical composition and soot precursors, and is applied at conditions that result in low temperature non-sooting combustion. Production of soot precursors is the first step toward production of soot, and modeling precursor production is expected to give insight into the overall evolution of soot inside the engine. The results of the analysis show that the model has been successful in describing many of the observed characteristics of low temperature combustion.

A detailed comparison of cylinder pressure derived combustion performance and engine-out emissions is made between an all-metal single-cylinder light-duty diesel engine and a geometrically equivalent engine designed for optical accessibility. The metal and optically accessible single-cylinder engines have the same nominal geometry, including cylinder head, piston bowl shape and valve cutouts, bore, stroke, valve lift profiles, and fuel injection system. The bulk gas thermodynamic state near TDC and load of the two engines are closely matched by adjusting the optical engine intake mass flow and composition, intake temperature, and fueling rate for a highly dilute, low temperature combustion (LTC) operating condition with an intake O2 concentration of 9%. Subsequent start of injection (SOI) sweeps compare the emissions trends of UHC, CO, NOx, and soot, as well as ignition delay and fuel consumption.

Homogeneous Charge Compression Ignition (HCCI) combustion is a process dominated by chemical kinetics of the fuel-air mixture. The hottest part of the mixture ignites first, and compresses the rest of the charge, which then ignites after a short time lag. Crevices and boundary layers generally remain too cold to react, and result in substantial hydrocarbon and carbon monoxide emissions. Turbulence has little effect on HCCI combustion, and may be most important as a factor in determining temperature gradients and boundary layer thickness inside the cylinder. The importance of thermal gradients inside the cylinder makes it necessary to use an integrated fluid mechanics-chemical kinetics code for accurate predictions of HCCI combustion. However, the use of a fluid mechanics code with detailed chemical kinetics is too computationally intensive for today's computers.

We have developed a methodology for predicting combustion and emissions in a Homogeneous Charge Compression Ignition (HCCI) Engine. This methodology combines a detailed fluid mechanics code with a detailed chemical kinetics code. Instead of directly linking the two codes, which would require an extremely long computational time, the methodology consists of first running the fluid mechanics code to obtain temperature profiles as a function of time. These temperature profiles are then used as input to a multi-zone chemical kinetics code. The advantage of this procedure is that a small number of zones (10) is enough to obtain accurate results. This procedure achieves the benefits of linking the fluid mechanics and the chemical kinetics codes with a great reduction in the computational effort, to a level that can be handled with current computers.

Engine operation with blended SRC-II and pyridine doped diesel fuel were compared relative to regular #2 diesel fuel in a 4-stroke, turbocharged, direct injection, high speed commercial diesel engine. The brake specific fuel consumption, (M-Joule/hp-hr), turbocharging, combustion characteristics and smoke did not change between blended SRC-II and regular #2 diesel fuel. This was expected since the sample fuels were blended to be of the same cetane number. The maximum torque, hydrocarbon and NOx emissions were higher for blended SRC-II. There was essentially no difference in the NOx measurements of the pyridine doped fuel and regular #2 diesel fuel. The NOx emission increase for the blended SRC-II is believed to be caused by the increased aromatic content of the blended SRC-II and not the fuel nitrogen conversion.

A Texaco L-163S TCCS (Texaco Controlled Combustion System) engine was operated with pure methanol to investigate the origin and mechanism of unburned fuel (UBF) and formaldehyde emissions. The effects of engine load, speed and coolant temperature on the exhaust emissions were studied using both continuous and time-resolved sampling methods. Within the range studied, increasing the engine load resulted in a decrease of the exhaust UBF emissions and an increase in the formaldehyde emissions. Engine speed had little effect on both UBF and formaldehyde emissions. Decreasing the engine coolant temperature from 85°C to 45°C caused the exhaust UBF emissions to approximately double and the formaldehyde emission to increase approximately 20 percent. It is hypothesized that both fuel impingement and spray tailing are responsible for the high UBF emissions. In-cylinder formation of formaldehyde was found to be the major source of the exhaust aldehyde emissions in this experiment.

This research work has focused on measuring the effect of fuel/air mixing on performance and emissions for a homogeneous charge compression ignition engine running on propane. A laser instrument with a high-velocity extractive probe was used to obtain time-resolved measurements of the fuel concentration both at the intake manifold and from the cylinder for different levels of fuel-air mixing. Cylinder pressure and emissions measurements have been performed at these mixing levels. From the cylinder pressure measurements, the IMEP and peak cylinder pressure were found. The fuel-air mixing level was changed by adding the fuel into the intake system at different distances from the intake valve (40 cm and 120 cm away). It was found that at the intake manifold, the fuel and air were better mixed for the 120 cm fuel addition location than for the 40 cm location.

Deviations between transient and steady state operation of a modern light duty diesel engine were identified by comparing rapid load transitions to steady state tests at the same speeds and fueling rates. The validity of approximating transient performance by matching the transient charge air flow rate and intake manifold pressure at steady state was also assessed. Results indicate that for low load operation with low temperature combustion strategies, transient deviations of MAF and MAP from steady state values are small in magnitude or short in duration and have relatively little effect on transient engine performance. A new approximation accounting for variations in intake temperature and excess oxygen content of the EGR was more effective at capturing transient emissions trends, but significant differences in magnitudes remained in certain cases indicating that additional sources of variation between transient and steady state performance remain unaccounted for.

Multiple injection strategies have been revealed as an efficient means to reduce diesel engine NOx and soot emissions simultaneously, while maintaining or improving its thermal efficiency. Empirical soot models widely adopted in engine simulations have not been adequately validated to predict soot formation with multiple injections. In this work, a multiple-step phenomenological (MSP) soot model that includes particle inception, surface growth, oxidation, and particle coagulation was revised to better describe the physical processes of soot formation in diesel combustion. It was found that the revised MSP model successfully reproduces measured soot emission dependence on the start-of-injection timing, while the two-step empirical and the original MSP soot models were less accurate. The revised MSP model also predicted reasonable soot and intermediate species spatial profiles within the combustion chamber.

Homogeneous charge compression ignition (HCCI) has received much attention in recent years due to its ability to reduce both fuel consumption and NO emissions compared to normal spark-ignited (SI) combustion. However, due to the limited operating range of HCCI, production feasible engines will need to employ a combination of combustion strategies, such as stoichiometric SI combustion at high loads and leaner burn spark-assisted compression ignition (SACI) and HCCI at intermediate and low loads. The goal of this study was to extend the high load limit of HCCI into the SACI region while maintaining a stoichiometric equivalence ratio. Experiments were conducted on a single-cylinder research engine with fully flexible valve actuation. In-cylinder pressure rise rates and combustion stability were controlled using cooled external EGR, spark assist, and negative valve overlap. Several engine loads within the SACI regime were investigated.

A kinetic carbon monoxide (CO) emission model is developed to simulate engine out CO emissions for conventional diesel combustion. The model also incorporates physics governing CO emissions for low temperature combustion (LTC). The emission model will be used in an integrated system level model to simulate the operation and interaction of conventional and low temperature diesel combustion with aftertreatment devices. The Integrated System Model consists of component models for the diesel engine, engine-out emissions (such as NOx and Particulate Matter), and aftertreatment devices (such as DOC and DPF). The addition of CO emissions model will enhance the capability of the Integrated System Model to predict major emission species, especially for low temperature combustion. In this work a CO emission model is developed based on a two-step global kinetic mechanism [8].

Accurate and useful mathematical models of physical processes can be made when we understand all of the phenomena involved. This paper reviews our understanding of the fluid flow, heat transfer and thermodynamic processes occurring in engines and the status of mathematical models expressing this understanding. Thermodynamic single system rate models are found to be extremely useful in predicting power and fuel consumption performance but of limited value in predicting emission performance. Multiple-zone, nonequilibrium models are essential for predicting emissions but are limited in accuracy by computer capacity and our understanding of engine phenomena which vary rapidly both with space and time. The need for and ability of new types of instrumentation, primarily optical, to increase our understanding of engine phenomena and improve our models is discussed.

Detailed characteristics of morphology, nanostructures, and sizes were analyzed for particulate matter (PM) emissions from low-temperature combustion (LTC) modes of a single-cylinder, light-duty diesel engine. The LTC engines have been widely studied in an effort to achieve high combustion efficiency and low exhaust emissions. Recent reports indicate that the number of nucleation mode particles increased in a broad engine operating range, which implies a negative impact on future PM emissions regulations in terms of the nanoparticle number. However, the size measurement of solid carbon particles by commercial instruments is indeed controversial due to the contribution of volatile organics to small nanoparticles. In this work, an LTC engine was operated with various biofuel blends, such as blends (B20) of soy bean oil (soy methyl ester, SME20) and palm oil (palm methyl ester, PME20), as well as an ultra-low-sulfur diesel fuel.

A spectroscopic diagnostic system was designed to study the effects of different engine parameters on the chemiluminescence characteristic of HCCI combustion. The engine parameters studied in this work were intake temperature, fuel delivery method, fueling rate (load), air-fuel ratio, and the effect of partial fuel reforming due to intake charge preheating. At each data point, a set of time-resolved spectra were obtained along with the cylinder pressure and exhaust emissions data. It was determined that different engine parameters affect the ignition timing of HCCI combustion without altering the reaction pathways of the fuel after the combustion has started. The chemiluminescence spectra of HCCI combustion appear as several distinct peaks corresponding to emission from CHO, HCHO, CH, and OH superimposed on top of a CO-O continuum. A strong correlation was found between the chemiluminescence light intensity and the rate of heat release.

Simulations of DI Diesel engine combustion have been performed using a modified KIVA-II package with a recently developed phenomenological soot model. The phenomenological soot model includes generic description of fuel pyrolysis, soot particle inception, coagulation, and surface growth and oxidation. The computational results are compared with experimental data from a Cummins N14 single cylinder test engine. Results of the simulations show acceptable agreement with experimental data in terms of cylinder pressure, rate of heat release, and engine-out NOx and soot emissions for a range of fuel injection timings considered. The numerical results are also post-processed to obtain time-resolved soot radiation intensity and compared with the experimental data analyzed using two-color optical pyrometry. The temperature magnitude and KL trends show favorable agreement.

The applicability of several popular diesel particulate matter (PM) measurement techniques to low temperature combustion is examined. The instruments' performance in measuring low levels of PM from advanced diesel combustion is evaluated. Preliminary emissions optimization of a high-speed light-duty diesel engine was performed for two conventional and two advanced low temperature combustion engine cases. A low PM (<0.2 g/kg_fuel) and NOx (<0.07 g/kg_fuel) advanced low temperature combustion (LTC) condition with high levels of exhaust gas recirculation (EGR) and early injection timing was chosen as a baseline. The three other cases were selected by varying engine load, injection timing, injection pressure, and EGR mass fraction. All engine conditions were run with ultra-low sulfur diesel fuel. An extensive characterization of PM from these engine operating conditions is presented.

Experimentally obtained energy release results, a semi-empirical ignition model, and an empirical energy release equation developed during this research were used to evaluate the combustion of compression-ignited homogeneous mixtures of fuel, air, and exhaust products in a CFR engine. A systematic study was carried out to evaluate the response of compression-ignited homogeneous charge (CIHC) combustion to changes in operating parameters with emphasis being placed on the phenomena involved rather than the detailed chemical kinetics. This systematic study revealed that the response of the combustion process to changes in operating parameters can be explained in terms of known chemical kinetics, and that through the proper use of temperature and species concentrations the oxidation kinetics of hydrocarbon fuels can be sufficiently controlled to allow an engine to be operated in a compression-ignited homogeneous charge combustion mode.

In current systems, for a given nozzle and injection pressure (pump speed), the shape of the injection rate is fixed and the injection timing is the only variable the engine designer can vary. For this non-interactive injection system, changing the injector nozzle (number and diameter of holes) will proportionately change the injection shape. New injection systems in which the rate of injection is a controlled variable are being developed. Results from one such injector, called the UCORS (Universal Combustion Optimization and Rate Shaping), are reported in this paper. The system can dynamically control its injection rate shape by controlling the position and size of a pilot injection relative to the main injection. Data and analysis from an out-of-engine and combustion chamber study of the UCORS injection system are presented.

A dilution source sampling system has been incorporated into the exhaust measurement system of a research single-cylinder diesel engine. To allow more detailed assessment of the individual chemical components of the diesel particulate matter (PM) the exhaust dilution system includes a residence time chamber (RTC) to allow for residence times of 30 to 60 seconds in the second stage of dilution before sampling. Samples are collected on a range of different filters where mass loading, elemental and organic carbon (ECOC), trace metals, sulfate ions (SO4), particle-phase organic compounds, and semi-volatile organic compounds are evaluated. In addition, particle size distributions have been determined using a scanning mobility particle sizer (SMPS). Results show that the chemical composition of the particulate matter is highly dependent on the engine operating conditions.