Search Results

Particle Swarm and the Genetic Algorithm were coupled to optimize multiple performance metrics for the combustion of neat biodiesel in a turbocharged, four cylinder, John Deere engine operating under constant partial load. The enhanced algorithm was used with five inputs including EGR, injection pressure, and the timing/distribution of fuel between a pilot and main injection. A merit function was defined and used to minimize five output parameters including CO, NOx, PM, HC and fuel consumption simultaneously. The combination of PSO and GA yielded convergence to a Pareto regime without the need for excessive engine runs. Results along the Pareto front illustrate the tradeoff between NOx and particulate matter seen in the literature.

An integrated transient engine simulation methodology has been developed to allow the calculation of a thermal shock as it propagates in time through the engine structure. It links, in a fully consistent way, a very comprehensive thermodynamic model of in-cylinder processes, including a detailed gas-phase heat transfer representation, with a turbocharger/air flow/plenum model and a finite element model of the structure. The methodology tracks the turbocharger boost increase and the cycle-by-cycle build-up of in-cylinder heat transfer during engine load and speed changes, producing a transient thermal response in the structure, until new steady-state is reached. The presented results highlight the calculated transient engine performance response and the thermal and stress response of various metal and ceramic components during sudden speed and load changes in heavy duty diesel engines.

An integrated numerical model has been developed for diesel engine computations based on the KIVA-II code. The model incorporates a modified RNG k-ε, turbulence model, a ‘wave’ breakup spray model, the Shell ignition model, the laminar-and-turbulent characteristic-time combustion model, a crevice flow model, a spray/wall impingement model that includes rebounding and breaking-up drops, and other improved submodels in the KIVA code. The model was validated and applied to model successfully different types of diesel engines under various operating conditions. These engines include a Caterpillar engine with different injection pressures at different injection timings, a small Tacom engine at different loads, and a Cummins engine modified by Sandia for optical experiments. Good levels of agreement in cylinder pressures and heat release rate data were obtained using the same computer model for all engine cases.

Numerical models were used to study the effects of dimethyl ether (DME) on the operation of a compression-ignition engine fueled with premixed natural gas. The models used multi-dimensional engine CFD coupled with detailed chemical kinetics. Combustion characteristics of various compositions of the natural gas and DME mixture were simulated. Results showed that combustion phasing, nitrogen oxides emissions, and effects of fuel compositions on engine operating limits were well predicted. Chemical kinetics analysis indicated that ignition was achieved by DME oxidation, which, in turn, induced natural gas combustion. It was found that low temperature heat release became more significant as DME concentration increased. For an appropriate amount of DME in the mixture, the stable engine operating range became narrower as natural gas concentration increased. The model also captured the low temperature combustion features of the present engine with low nitrogen oxides emissions.

The strategy of variable Intake Valve Closure (IVC) timing, as a means to improve performance and emission characteristics, has gained much acceptance in gasoline engines; yet, it has not been explored extensively in diesel engines. In this study, genetic algorithms are used in conjunction with the multi-dimensional engine simulation code KIVA-3V to investigate the optimum operating variables for a typical heavy-duty diesel engine working with late IVC. The effects of start-of-injection timing, injection duration and exhaust gas recirculation were investigated along with the intake valve closure timing. The results show that appreciable reductions in NOx+HC (∼82%), soot (∼48%) and BSFC (∼7.4%) are possible through this strategy, as compared to a baseline diesel case of (NOx+HC) = 9.48g/kW-hr, soot = 0.17 g/kW-hr and BSFC = 204 g-f/kW-hr. The additional consideration of double injections helps to reduce the high rates of pressure rise observed in a single injection scheme.

The impact of fuel droplets on heated surfaces is of great importance in internal combustion engines. In engine computational fluid dynamics (CFD) simulations, the drop-wall interaction is usually considered by using models derived from experimental data and correlations rather than direct simulations. This paper presented a numerical method based on smoothed particle hydrodynamics (SPH), which can directly simulate the impact process of fuel droplets impinging on solid surfaces. The SPH method is a Lagrangian meshfree particle method. It discretizes fluid into a number of SPH particles and governing equations of fluid into a set of particle equations. By solving the particle equations, the movement of particles can be obtained, which represents the fluid flows. The SPH method is able to simulate the large deformation and breakup of liquid drops without using additional interface tracking techniques.

This study considers combustion processes in a heavy-duty diesel engine at various low emissions operating conditions. The start-of-injection timings varied from -20 to 5 ATDC while the EGR levels varied from 6% to 44%. At certain conditions, HCCI-like combustion characteristics were observed under which low emissions could be achieved. The numerical model used is an improved version of KIVA-3V that can simulate spray breakup and mixture autoignition over a wide range of conditions. The ignition and combustion processes were simulated using both detailed and standard (simplified) chemistry models. Model results show that engine combustion and emissions can be predicted reasonably well under the current conditions. The trends of NOx and soot emissions with respect to the injection timings and EGR levels were well captured. However, it was found that the model over-predicted the NOx emissions in certain early injection cases.

Managing the injection rate profile is a powerful tool to control engine performance and emission levels. In particular, Common Rail (C.R.) injection systems allow an almost completely flexible fuel injection event in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection and, in the near future, multiple injections. This research deals with the development of a network-based numerical tool for understanding operating condition limits of the Common Rail injector. The models simulate the electro-fluid-mechanical behavior of the injector accounting for cavitation in the nozzle holes. Validation against experiments has been performed. The model has been used to provide insight into the operating conditions of the injector and in order to highlight the application to injection system design.

Diesel engine control has already become complex, and in order to meet future emissions standards (such as Euro 4) it is likely to be the control system that will provide the needed performance increment. Common rail fuel injection offers yet more degrees of freedom which will need to be exploited as new emissions standards emerge. Whatever the emissions standards, there is a need to reduce risk at the earliest stages in the development of the powertrain. This will involve early and extensive simulation of the powertrain including its control system, sensors and actuators. What is the best way to achieve this using current tools? The result lies in a combination of a phenomenological model of the engine and a flexible controls environment. To illustrate the principles of developing prototype control systems, we will use the example of the CPower environment, which is a combination of a detailed engine simulation code (GT-Power) and the Simulink simulation environment.

Detailed chemical kinetics was implemented in the KIVA-3V multidimensional CFD code to study the combustion process in Homogeneous Charge Compression Ignition (HCCI) engines. The CHEMKIN code was implemented such that the chemistry and flow solutions were coupled. Detailed reaction mechanisms were used to simulate the fuel chemistry of ignition and combustion. Effects of turbulent mixing on the reaction rates were also considered. The model was validated using the experimental data from two modified heavy-duty diesel engines, including a Volvo engine and a Caterpillar engine operated at the HCCI mode. The results show that good levels of agreement were obtained using the present KIVA/CHEMKIN model for a wide range of engine conditions, including various fuels, injection systems, engine speeds, and EGR levels. Ignition timings were predicted well without the need to adjust any kinetic constants.

The combustion and emissions of a diesel/natural gas dual-fuel engine are studied. Available engine experimental data demonstrates that the dual-fuel configuration provides a potential alternative to diesel engine operation for reducing emissions. The experiments are compared to multi-dimensional model results. The computer code used is based on the KIVA-3V code and consists of updated sub-models to simulate more accurately the fuel spray atomization, auto-ignition, combustion and emissions processes. The model results show that dual-fuel engine combustion and emissions are well predicted by the present multi-dimensional model. Significant reduction in NOx emissions is observed in both the experiments and simulations when natural gas is substituted for diesel fuel. The HC emissions are under predicted by numerical model as the natural gas substitution is increased.

Accurate modeling of evaporating sprays is critical for diesel engine simulations. The standard spray and evaporation models in KIVA-3V tend to under-predict the vapor penetration, especially at high ambient pressure conditions. A sharp decrease of vapor penetration gradient is observed soon after the liquid spray is completely evaporated due to the lack of momentum sources beyond the liquid spray region. In this study, a gas particle model is implemented in KIVA-3V which tracks the momentum sources resulting from the evaporated spray. Lagrangian tracking of imaginary gas particles is considered until the velocity of the gas particle is comparable to that of the gas phase velocity. The gas particle continuously exchanges momentum with the gas phase and as a result the vapor penetrations are improved. The results using the present gas particle model is compared with experimental data over a wide range of ambient conditions and good levels of agreement are observed in vapor penetration.

Numerical simulations were performed to investigate the combustion process in the Premixed Compression Ignition (PCI) regime in a light-duty diesel engine. The CHEMKIN code was implemented into an updated KIVA-3V release 2 code to simulate combustion and emission characteristics using reduced chemistry. The test engine used for validation data was a single cylinder version of a production 1.9L four-cylinder HSDI diesel engine. The engine operating condition considered was 2,000 rev/min and 5 bar BMEP load. Because high EGR levels are required for combustion retardation to make PCI combustion possible, the EGR rate was set at a relatively high level (40%) and injection timing sweeps were considered. Since injection timings were very advanced, impingement of the fuel spray on the piston bowl wall was unavoidable. To model the effects of fuel films on exhaust emissions, a drop and wall interaction model was implemented in the present code.

Combustion in an HSDI diesel engine using different injectors to realize low emissions is modeled using detailed chemical kinetics in this study. Emission characteristics of the engine are investigated using injectors that have different included spray angles, ranging from 50 to 130 degrees. The engine was operated under PCCI conditions featuring early injection times, high EGR levels and high intake temperatures. The Representative Interactive Flamelet (RIF) model was used with the KIVA code for combustion and emission modeling. Modeling results show that spray targeting plays an important role in determining the in-cylinder mixture distributions, which in turn affect the resulting pollutant emissions. High soot emissions are observed for injection conditions that result in locally fuel rich regions due to spray impingement normal to the piston surface.

An image acquisition-and-processing camera system was developed for in-cylinder diagnostics of a single-cylinder heavy duty diesel engine. The engine was equipped with an electronically-controlled common-rail fuel injection system that allowed both single and split (multiple) injections to be studied. The imaging system uses an endoscope to acquire luminous flame images from the combustion chamber and ensures minimum modification to the engine geometry. The system also includes an optical linkage, an image intensifier, a CID camera, a frame grabber, control circuitry and a computer. Experiments include both single and split injection cases at 90 MPa and 45 MPa injection pressures at 3/4 load and 1600 rev/min with simulated turbocharging. For the single injection at high injection pressure (90 MPa) the results show that the first luminous emissions from the ignition zone occur very close to the injector exit followed by rapid luminous flame spreading.

A new model for radiation heat transfer in DI diesel engines has been developed. The model calculates the heat transfer rates as a function of the instantaneous values of the radiation zone size, radiation temperature, and of the absorption coefficient of the soot-laden gas. The soot concentration levels are calculated from kinetic expressions for soot formation and burnup. The spatial distribution of the radiant heat flux along the combustion chamber walls is calculated by a zonal model. The model has been applied to a conventional heavy duty highway DI diesel engine to generate predictions over a range of engine speeds and loads. These predictions indicated a wide variation in the ratio of radiation to the total heat transfer, ranging from less than ten percent to more than thirty percent, depending on the speed and load.

The present study investigated HCCI combustion in a heavy-duty diesel engine both experimentally and numerically. The engine was equipped with a hollow-cone pressure-swirl injector using gasoline direct injection. Characteristics of HCCI combustion were obtained by very early injection with a heated intake charge. Experimental results showed an increase in NOx emission and a decrease in UHC as the injection timing was retarded. It was also found that optimization can be achieved by controlling the intake temperature together with the start-of-injection timing. The experiments were modeled by using an engine CFD code with detailed chemistry. The CHEMKIN code was implemented into KIVA-3V such that the chemistry and flow solutions were coupled. The model predicted ignition timing, cylinder pressure, and heat release rates reasonably well. The NOx emissions were found to increase as the injection timing was retarded, in agreement with experimental results.

An experimental study was conducted of the heat radiation in a single-cylinder direct injection 142 diesel engine. The engine was operated at speeds ranging from 1000 to 2100 RPM and a variety of loads. The radiation was measured using a specially designed fiber-optics probe operating on the two-color principle. The probe was located in the head at two different locations: in one location it faced the piston bowl and in the other it faced the piston crown. The data obtained from the probe was processed to deduce the apparent radiation temperature and soot volume concentration as a function of crank angle. The resultant profiles of radiation temperature and of the soot volume concentrations were compared with the predictions of a zonal heat radiation model imbedded in a detailed two-zone thermodynamic cycle code. The agreement between the model and the measurements was found to be good, both in trends and in magnitudes.

A comprehensive diesel engine system model, representing in detail engine heat transfer processes, has been applied to a study of insulated diesel engines. The study involved a broad design analysis matrix covering a range of engine configurations with and without inter-cooling and exhaust heat recovery devices, three operating conditions and seven heat rejection packages. The main findig of this study is that the retained heat conversion efficiency (RHCE), of the in-cylinder heat retained by insulation to piston work, is 35-40 percent; these levels of RHCE are larger than those predicted by previous models. This means that a significant part of the retained heat is converted directly to piston work rather than being merely available in the exhaust stream, from which it would be recoverable with a much lower efficiency.

Various mixtures of ammonia (NH₃) and dimethyl ether (DME) were tested in a diesel engine to explore the feasibility of using ammonia as an alternative, non-carbon fuel to mitigate greenhouse gas emissions. The original diesel fuel injection system was replaced with a new system for injecting ammonia-DME mixtures into the cylinder directly. The injection pressure was maintained at approximately 206 bar for various fuel mixtures including 100% DME, 60%DME-40%NH₃, and 40%DME-60%NH₃ (by weight). As ammonia content was increased in the fuel mixture, the injection timing needed to be advanced to ensure successful engine operation. It was found that cycle-to-cycle variation increased significantly when 40%DME-60%NH₃ was used. In the meantime, combustion of 40%DME-60%NH₃ exhibited HCCI characteristics as the injection timing ranged from 90 to 340 before top-dead-center (BTDC). Emissions data show that soot emissions remained extremely low for the fuel mixtures tested.