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In a recent study, quantitative measurements were presented of in-cylinder spatial distributions of mixture equivalence ratio in a single-cylinder light-duty optical diesel engine, operated with a non-reactive mixture at conditions similar to an early injection low-temperature combustion mode. In the experiments a planar laser-induced fluorescence (PLIF) methodology was used to obtain local mixture equivalence ratio values based on a diesel fuel surrogate (75% n-heptane, 25% iso-octane), with a small fraction of toluene as fluorescing tracer (0.5% by mass). Significant changes in the mixture's structure and composition at the walls were observed due to increased charge motion at high swirl and injection pressure levels. This suggested a non-negligible impact on wall heat transfer and, ultimately, on efficiency and engine-out emissions.

This paper shows how a computer can systematically remove non-essential chemical reactions from a large chemical kinetic mechanism. The computer removes the reactions based upon a single solution using a detailed mechanism. The resulting reduced chemical mechanism produces similar numerical predictions significantly faster than predictions that use the detailed mechanism. Specifically, a reduced chemical kinetics mechanism for iso-octane has been derived from a detailed mechanism by eliminating unimportant reaction steps and species. The reduced mechanism has been developed for the specific purpose of fast and accurate prediction of ignition timing in an HCCI engine. The reduced mechanism contains 199 species and 383 reactions, while the detailed mechanism contains 859 species and 3606 reactions. Both mechanisms have been used in numerical simulation of HCCI combustion.

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.

A droplet vaporization model has been developed for use in high pressure spray modeling. The model is a modification of the common Spalding vaporization model that accounts for the effects of high pressure on phase equilibrium, transport properties, and surface tension. The new model allows for a nonuniform temperature within the liquid by using a simple 2-zone model for the droplet. The effects of the different modifications are tested both for the case of a single vaporizing droplet in a quiescent environment as well as for a high pressure spray using the KIVA II code. Comparisons with vaporizing spray experiments show somewhat improved spray penetration predictions. Also, the effect of the vaporization model on diesel combustion predictions was studied by applying the models to simulate the combustion process in a heavy duty diesel engine. In this case the standard and High Pressure vaporization models were found to give similar heat release and emissions results.

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.

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.

A transport equation residual model incorporating refined G-equation and detailed chemical kinetics combustion models has been developed and implemented in the ERC KIVA-3V release2 code for Gasoline Direct Injection (GDI) engine simulations for better predictions of flame propagation. In the transport equation residual model a fictitious species concept is introduced to account for the residual gases in the cylinder, which have a great effect on the laminar flame speed. The residual gases include CO2, H2O and N2 remaining from the previous engine cycle or introduced using EGR. This pseudo species is described by a transport equation. The transport equation residual model differentiates between CO2 and H2O from the previous engine cycle or EGR and that which is from the combustion products of the current engine cycle.

We have applied an imaging system to a spray in an engine-fed combustion bomb to investigate some of the features of diesel spray ignition. A high pressure electronic unit injector with main and pilot injection features was used. Our interest in this work was the local air/fuel ratio, particularly in the vicinity of the spray plumes. The measurement was made by seeding the air in the intake manifold with biacetyl. A tripled ND:YAG laser causes the biacetyl to fluoresce with a signal that is proportional to its local concentration. The biacetyl partial pressure was carefully controlled, enabling approximate estimates of the local stoichiometry in the fuel spray. Twenty-four different cases were sampled. Parameters varied include swirl ratio, fuel quantity, number of holes in the fuel nozzle and distribution of fuel quantities in the pilot and main injections. This paper presents the results of three of these cases.

The simulation of combustion chemistry in internal combustion engines is challenging due to the need to include detailed reaction mechanisms to describe the engine physics. Computational times needed for coupling full chemistry to CFD simulations are still too computationally demanding, even when distributed computer systems are exploited. For these reasons the present paper proposes a time scale separation approach for the integration of the chemistry differential equations and applies it in an engine CFD code. The time scale separation is achieved through the estimation of a characteristic time for each of the species and the introduction of a sampling timestep, wherein the chemistry is subcycled during the overall integration. This allows explicit integration of the system to be carried out, and the step size is governed by tolerance requirements.

A turbulent combustion model based on the coherent flamelet model was developed in this study and applied to diesel engines. The combustion was modeled in three distinct but overlapping phases: low temperature ignition kinetics using the Shell ignition model, high temperature premixed burn using a single step Arrhenius equation, and the flamelet based diffusion burn. Two criteria for transitions based on temperature, heat release rate, and the local Damköhler number were developed for the progression of combustion between each of these phases. The model was implemented into the computational computer code KIVA-II. Previous experiments on a Caterpillar model E 300, # 1Y0540 engine, a Tacom LABECO research engine, and a single cylinder version of a Cummins N14 production engine were used to validate the cylinder averaged predictions of the model.

This paper investigates the dynamic errors between the commonly used two-lump mass connecting rod model and the actual connecting rod model for the internal combustion engine. Because of the errors between the actual rod inertia and this simplified two-lump mass model, incorrect engine dynamics and internal forces are often predicted. In this paper, the magnitudes of force differences related to errors of connecting rod inertia are presented for various engines at different engine operating speeds. A method to predict the maximum side force and its maximum deviation is presented. And the technique to minimize variability in connecting rod mass and moment of inertia, as well as minimizing errors in the lumped mass model commonly used in industry are also introduced to avoid incorrect engine dynamics and internal forces.

A new technique which is based on optoacoustic phenomena has been developed for measuring in-cylinder gas temperature and turbulent diffusivity. In the experiments, a high energy Nd:YAG pulsed laser beam was focused to cause local ionization of air at a point in the combustion chamber. This initiates a shock wave and creates a hot spot. The local temperature and turbulent diffusivity are determined by monitoring the shock propagation and the hot spot growth, respectively, with a schlieren photography system. In order to assess the validity and accuracy of the measurements, the technique was also applied to a turbulent jet. The temperature measurements were found to be accurate to within 3%. Results from the turbulent jet measurements also showed that the growth rate of the hot spot diameter can be used to estimate the turbulent diffusivity. In-cylinder gas temperature measurements were made in a motored single cylinder Caterpillar diesel engine, modified for optical access.

In-cylinder thermal barrier coatings (TBCs) have the capability to reduce fuel consumption by reducing wall heat transfer and to increase exhaust enthalpy. Low thermal conductivity, low volumetric heat capacity thermal barrier coatings tend to reduce the gas-wall temperature difference, the driving potential for heat transfer from the gas to the combustion chamber surfaces. This paper presents a coupling between an analytical methodology for multi-layer coated wall surface temperature prediction with a fully calibrated production model in a commercial system-level simulation software package (GT-Power). The wall surface temperature at each time step was calculated efficiently by convolving the engine wall response function with the time-varying surface boundary condition, i. e., in-cylinder heat flux and coolant temperature. This tool allows the wall to be treated either as spatially uniform with one set of properties, or with independent head/piston/liner components.

Diesel piston bowl geometry can affect turbulent mixing and therefore it impacts heat-release rates, thermal efficiency, and soot emissions. The focus of this work is on the effects of bowl geometry and injection timing on turbulent flow structure. This computational study compares engine behavior with two pistons representing competing approaches to combustion chamber design: a conventional, re-entrant piston bowl and a stepped-lip piston bowl. Three-dimensional computational fluid dynamics (CFD) simulations are performed for a part-load, conventional diesel combustion operating point with a pilot-main injection strategy under non-combusting conditions. Two injection timings are simulated based on experimental findings: an injection timing for which the stepped-lip piston enables significant efficiency and emissions benefits, and an injection timing with diminished benefits compared to the conventional, re-entrant piston.

Two distinct atomization strategies are contrasted through the measurement of time and spatially dependent mass flux. The two systems investigated include a pressure atomizer (6.9 MPa opening pressure) and an air-assist atomizer. Both systems have potential for use in direct injection spark ignition engines. The mass flux data presented were obtained using a spray patternator that was developed to allow phased sampling of the spray. The temporal mass related history of the spray was reconstructed as volume versus time plots and interpolated mass flux contour plots. Results indicate substantial differences in the distribution of both mass and mass flux in space and time for the two injection systems. For example, the pressure atomizer at high mass delivery rates produced a spray that collapsed into a dispersed cylindrical shape while at low rates, generated a hollow cone structure.

In this work, linear, non-linear and a generalized renormalization group (RNG) two-equation RANS turbulence models of the k-epsilon form were compared for the prediction of turbulent compressible flows in diesel engines. The object-oriented, multidimensional parallel code FRESCO, developed at the University of Wisconsin, was used to test the alternative models versus the standard k-epsilon model. Test cases featured the academic backward facing step and the impinging gas jet in a quiescent chamber. Diesel engine flows featured high-pressure spray injection in a constant volume vessel from the Engine Combustion Network (ECN), as well as intake flows in a high-swirl diesel engine. For the engine intake flows, a model of the Sandia National Laboratories 1.9L light-duty single cylinder optical engine was used.

This paper presents the results of an experimental program in which a Texaco L-163S engine was fueled with methanol and operated in its traditional stratified charge mode and then modified to run as a homogeneous charge spark ignited engine. The primary data taken were the aldehyde and unburned fuel emissions (UBF). These data were taken using a continuous time-averaging sampling probe at the exhaust tank and at the exhaust port and with a rotary time-resolving sampling valve located at the exhaust port. The data are for two loads, 138.1 kPa (20 psi) and 207.1 kPa (30 psi) BMEP and three speeds, 1000, 1400 and 1800 rpm. The data indicate that for both the stratified charge and the homogeneous charge modes of operation formaldehyde was the only aldehyde detected in the exhaust and it primarily originated in the cylinder.

This paper describes the Homogeneous charge compression ignition (HCCI) research activities being currently pursued at Lawrence Livermore National Laboratory and at the University of California Berkeley. Current activities include analysis as well as experimental work. HCCI is an old combustion technology that may now be developed with expectations of high efficiency, low NOx, and low particulate matter emissions; in short, an alternative to diesel engines. On analysis, we have developed two powerful tools: a single zone model and a multi-zone model. The single zone model has proven very successful in predicting start of combustion and providing reasonable estimates for peak cylinder pressure, indicated efficiency and NOX emissions. This model is being applied to develop detailed engine performance maps and control strategies, and to analyze the problem of engine startability.

Off-highway mining and construction equipment typically converts all the power output of the engine to hydraulic power, with this power then used to perform the earth-moving operations, and also to propel the vehicle. This equipment presents significant opportunities for a new type of powerplant designed to deliver hydraulic power directly. An alternative to the conventional engine driven pump is a free-piston engine-pump (FPEP). The FPEP incorporates the functions of both an internal combustion engine and a hydraulic pump into a single, less-complex unit. The design presented in this paper utilizes two double-ended, reciprocating, opposed pistons, with combustion at one end of each piston and pumping at the opposite end. The opposed piston layout provides balance and also facilitates uniflow scavenging through intake and exhaust ports in the combustion section of the engine. An important feature of this FPEP design is the rebound accumulator circuit.

Using a low-speed high-torque (LSHT) pump/motor to provide the speed range and torque for a hydrostatic automobile offers a number of advantages over using a high-speed low-torque pump/motor, combined with a gear reducer. However, there appear to be no LSHT units commercially available that have true variable displacement capability. Because of this void, a variable displacement pump/motor has been designed and built that could provide a direct drive for each wheel of a hydrostatic automobile. The unit uses some components such as the cylinder block, piston and modified rotating case from a commercially available radial piston pump/motor. Initial preliminary testing of the pump/motor indicates that it has good efficiency and performance characteristics, and, with further development should be very attractive for automotive use. This paper focuses on the design and kinematics of the device.