Fuel Evaporation Model Research Articles

High Load (21 Bar IMEP) Dual Fuel RCCI Combustion Using Dual Direct Injection

Dual-fuel reactivity controlled compression ignition (RCCI) combustion has shown high thermal efficiency and superior controllability with low NOx and soot emissions. However, as in other low temperature combustion (LTC) strategies, the combustion control using low exhaust gas recirculation (EGR) or a high compression ratio at high load conditions has been a challenge. The objective of this work was to examine the efficacy of using dual direct injectors for combustion phasing control of high load RCCI combustion. The present computational work demonstrates that 21 bar gross indicated mean effective pressure (IMEP) RCCI is achievable using dual direct injection. The simulations were done using the KIVA3V-Release 2 code with a discrete multicomponent fuel evaporation model, coupled with sparse analytical Jacobian solver for describing the chemistry of the two fuels (iso-octane and n-heptane). In order to identify an optimum injection strategy a nondominated sorting genetic algorithm II (NSGA II), which is a multiobjective genetic algorithm, was used. The goal of the optimization was to find injection timings and mass splits among the multiple injections that simultaneously minimize the six objectives: soot, nitrogen oxide (NOx), carbon monoxide (CO), unburned hydrocarbon (UHC), indicated specific fuel consumption (ISFC), and ringing intensity. The simulations were performed for a 2.44 liter, heavy-duty engine with a 15:1 compression ratio. The speed was 1800 rev/min and the intake valve closure (IVC) conditions were maintained at 3.42 bar, 90 °C, and 46% EGR. The resulting optimum condition has 12.6 bar/deg peak pressure rise rate, 158 bar maximum pressure, and 48.7% gross indicated thermal efficiency. The NOx, CO, and soot emissions are very low.

An advanced combustion model coupled with detailed chemical reaction mechanism for D.I diesel engine simulation

A multi-dimensional computational fluid dynamics (CFD) modeling was conducted on a direct injection turbo-charged diesel engine based on KIVA-4 code under full and mid engine loads. Multi-component fuel evaporation model of KIVA-4 was used and coupled with advanced combustion chemistry to generate a multi-component fuel combustion model by integrating CHEMKIN II into the KIVA-4 code. As the coding schema of KIVA-4 in the case of data/parameter allocation, etc. was different compared to previous version of KIVA-3V, a considerable amount of FORTRAN programming was performed in order to develop a multi-component fuel combustion model. The developed combustion model was capable of modeling combustion process of number of chemical species as the components of direct injected liquid fuel. Comparing to the single component fuel combustion model, new model is capable of comprehensive combustion modeling of blend fuel and heavy hydro-carbon fuels. Furthermore, spray breakup and collision models were changed to more advanced Kelvin–Helmholtz and Rayleigh–Taylor (KH–RT) and O’Rourke models, respectively. The model was used to simulate direct injected diesel engine under full and mid engine loads at three engine speed conditions. Extracted temporal and spatial results for equivalence ratio distribution inside the combustion chamber showed that under full load condition, a considerable amount of fuel was trapped in piston bowl after initiation of the injection process where such fuel rich local regions provide the potential for production of higher soot emission. Mean value of the fuel concentration history showed that the ignition delay was increased under mid engine load at all engine speeds producing higher amounts of unburned hydro carbons and carbon monoxide. By reducing engine load and speed, output power was decreased as well. However, same trend was not reported for the indicated thermal efficiency as the middle engine speed in considered engine loads, had slightly higher efficiency.

Engine Emissions at Various Cetane Numbers with Exhaust Gas Recirculation

Typical engine fuels are blends of various fuels species, i.e., multi component. Thus, the original single component fuel vaporization model was replaced by a multi component fuel vaporization model .The model has been extended to model diesel sprays under typical diesel conditions, including the effect of fuel cetane number variation .Necessary modifications were carried out at the various cooling rates. Found the performance of the diesel engine under various cooling rates at various cetane numbers, also various quantities of exhaust gas was re circulated and found performance of the engine. I. Introduction: Air pollution is referred addition harmful foreign particles or additives to the atmospheric air. The most of air pollution to the atmospheric is contributed by automobile engine emissions. The main emissions from the auto motive engine are oxides of nitrogen, oxides of sulphur, carbon dioxide, carbon monoxide, suspended or particulate matter, unused oxygen, and un burnt hydro carbons. Each of these pollutants has their own evil effect on the environment. Hence many efforts are made and many researches have been conducting to reduce these emissions without effecting the performance of the engine. The cetane number is evaluated directly as a function of fuel composition. By using a blend of cetane (hexadecane) which has a cetane number of 100, and iso cetane(a-methyl-naphthalene) which has a cetane number of 0, it is possible to achieve blends with a wide range of cetane numbers. Moreover, the cetane numbers used in the ignition model are the local values of cetane number within the engine since the two components could be vaporizing at different rates due to their volatility differentials. Combustion - In diesel engines, a significant portion of combustion is thought to be mixing-controlled. Hence, inter actions between turbulence and chemical reactions have to be considered. A laminar-and-turbulent characteristic-time combustion model was used for the present study. The local time rate of change of the partial density of species m, due to conversion from one chemical species to another, is given by where Ym is the mass fraction of species m, Y*m is the local and instantaneous thermodynamic equilibrium value of the mass fraction, andح cis the characteristic time for the achievement of equilibrium. To predict thermodynamic equilibrium temperatures accurately, it is sufficient to consider seven species: fuel, 02, N2, CO2,CO, H2, and H20, and to assume that the characteristic time is the same for all seven. As was previously assumed for the ignition model, the two fuel species are combined into an effective fuel for the purposes of the present implementation of the combustion model.

A discrete multicomponent fuel evaporation model with liquid turbulence effects

A new approach to simultaneously account for finite thermal conductivity, finite mass diffusivity and turbulence effects within atomizing multicomponent liquid fuel sprays has been developed in this study. The main contribution of this paper is to incorporate the liquid turbulence effect in modeling the boundary layer heat and mass resistance during multi-component droplet evaporation. The finite conductivity model is based on an existing two-layer film theory, where the turbulence characteristics of the droplet are used to estimate the effective thermal conductivity. The present paper extends the two-layer film theory formulation to include multi-component mass diffusivities within the droplet liquid phase. In this model four regions are considered: the interior region of the droplet, droplet-side interface, gas-side interface, and the surrounding gas phase. Approximate solutions to the quasi-steady energy and mass transfer equations were used to derive an explicit expression for the heat and mass flux from the surrounding gas to the droplet–gas interface, and within the multi-component droplet. Extension of the model to high pressures using the Peng–Robinson equation of state is also considered. The validation study was carried out for a bi-component decane/hexadecane fuel, followed by application studies of complex gasoline–ethanol blended fuels evaporating in hot gas environments.

Integration of a discrete multi-component fuel evaporation model with a G-equation flame propagation combustion model and its validation

A discrete multi-component fuel evaporation model has been successfully integrated with a G-equation flame propagation combustion model. In the discrete multi-component fuel evaporation model, the individual components of the fuel during the evaporation process are tracked, and the characteristics of the fuel components are determined from fuel libraries. In the G-equation flame propagation combustion model, five improved sub-models developed previously by the authors are used. Two new methods that are necessary for the integration are proposed. To consider the change of local fuel vapor mixture composition, a ‘blending cetane number approach’ is proposed that formulates the relationship between the fuel vapor mixture cetane number and the mole fraction and cetane number of each component. With the mixture cetane number, the research octane number can be calculated locally, and with this research octane number, the flame speed can be calculated. In the combustion stage, a ‘group chemistry method’ is proposed in which one representative species can be selected to represent several fuel components that belong to the same chemical family. This treatment makes it possible to use a smaller size of multi-component fuel chemical kinetic mechanism. Each sub-model included in the integrated model was validated to see if the integration process was correct or not, and finally the integrated model was tested to model complicated gasoline direct injection engine cases. Simulations of single-droplet and spray evaporation with discrete multi-component fuel cases from normal evaporation to flash boiling were performed and compared with available experimental data. The match between simulations and experiments is excellent. The G-equation flame propagation combustion model was also validated with experimental data. Evaporation and the combustion process were simulated for a gasoline direct injection engine. The simulated in-cylinder pressures are in good agreement with the experimental data.

Modeling effect of the biodiesel mixing ratio on combustion and emission characteristics using a reduced mechanism of methyl butanoate

This paper describes a modeling study on the effects of the mixing ratio of biodiesel derived from rice on combustion and emission characteristics. In order to model ignition and combustion processes, a combined mechanism of methyl butanoate and n-heptane was used after modifying some reaction constants. The oxygen content of rice oil was maintained at the measured value (11 vol.%) by assuming that one mole of rice oil was composed of one mole of methyl butanoate and two moles of n-heptane. The fuel property library of the KIVA code was expanded to include physical properties such as density and surface tension of rice oil (i.e., biodiesel). In addition, a discrete multi-component fuel evaporation model was employed to model the fuel injection, atomization, and evaporation. Calculated pressure histories and carbon monoxide (CO) and hydrocarbon (HC) emissions of the present study agreed reasonably with experiments at a 100 MPa injection pressure and a 10° BTDC injection timing for D100, BD20, and BD40. However some discrepancies were observed in predicting nitrogen oxide (NOx) emissions. The effect of the start of injection timing on fuel consumption and CO emissions were also studied.

Multi-component fuel vaporization modelling and its effect on spray development in gasoline direct injection engines

A multi-component fuel vaporization model has been developed and implemented into an in-house multi-phase computational fluid dynamics flow solver simulating the flow, spray, and air-fuel mixing processes taking place in gasoline direct injection (GDI) engines. Multi-component fuel properties are modelled assuming a specified composition of pure hydrocarbons. High-pressure and -temperature effects, as well as gas solubility and compressibility, are considered. Remote droplet vaporization is initially investigated in order to quantify and validate the most appropriate vaporization model for conditions relevant to those realized with GDI engines. Phenomena related to the fuel injection system and pressure-swirl atomizer flow as well as the subsequent spray development are considered using an one-dimensional fuel injection equipment model predicting the wave dynamics inside the injection system, a Eulerian volume of fluid-based two-phase flow model simulating the liquid film formation process inside the injection hole of the swirl atomizer and a Lagrangian spray model simulating the subsequent spray development, respectively. The computational results are validated against experimental data obtained in an optical engine and include laser Doppler velocimetry measurements of the charge air motion in the absence of spray injection and charge coupled device images of the fuel spray injected during the induction stroke. The results confirm that fuel composition affects the overall fuel spray vaporization rate, but not significantly relative to other flow and heat transfer processes taking place during the engine operation.

Multidimensional Modeling of Fuel Effects and Split Injections on Diesel Engine Cold-Starting

A computational model has been developed for describing multicomponent fuel vaporization and ignition in diesel engines and was implemented in the KIVA-II computational e uid dynamics code. The model has been applied to understand diesel engine cold-starting and the parameters that signie cantly ine uence this phenomena. Typical diesel fuels are blends of various fuels species, i.e., multicomponent. Thus, the original single-component fuel vaporization model in KIVA-II was replaced by a multicomponent fuel vaporization model. Necessary modie cations were carried out in other spray submodels that describe droplet breakup and coalescence to account for multicomponent fuels. The autoignition process was modeled using a modie ed multistep kinetics Shell ignition model to account for fuel composition effects. The improved model was applied to simulate cold-starting in diesel engines. The effects of fuel residual left from previous cycles, injection timing, and duration were studied. Split injections, where a small pilot injection was introduced during the compression stroke, were found to have a signie cant and benee cial effect on cold-starting.

Development and testing of diesel engine CFD models

The development and validation of Computational Fluid Dynamic (CFD) models for diesel engine combustion and emissions is described. The complexity of diesel combustion requires simulations with many complex, interacting submodels in order to be successful. The review focuses on the current status of work at the University of Wisconsin Engine Research Center. The research program, which has been ongoing for over five years, has now reached the point where significant predictive capability is in place. A modified version of the KIVA code is used for the computations, with improved submodels for liquid breakup, drop distortion and drag, spray-wall impingement with rebounding, sliding and breaking-up drops, wall heat transfer with unsteadiness and compressibility, multistep kinetics ignition and laminar-turbulent characteristic time combustion models, Zeldovich NO x formation, and soot formation with Nagle-Strickland-Constable oxidation. The code also considers piston-cylinder-liner crevice flows and allows computations of the intake flow process in the realistic engine geometry with two moving intake valves. A multicomponent fuel vaporization model and a flamelet combustion model have also been implemented. Significant progress has been made using a modified RNG k-ε turbulence model. This turbulence model is capable of predicting the large-scale structures that are produced by the squish flows and generated by the spray. These flow structures have an important impact on the prediction of NO x formation since it is very sensitive to the local temperatures in the combustion chamber. Model validation experiments have been performed using a single-cylinder version of a heavy duty truck engine that features state-of-the-art high-pressure electronic fuel injection and emissions instrumentation. In addition to cylinder pressure, heat release, and emissions measurements, combustion visualization experiments have been performed using an endoscope system that takes the place of one of the exhaust valves. In-cylinder gas velocity (PIV) and gas temperature measurements have also been made in the motored engine using optical techniques. Modifications to the engine geometry for optical access were minimal, thus ensuring that the results represent the actual engine. Experiments have also been conducted to study the effect of injection characteristics, including injection pressure and rate, nozzle inlet condition and multiple injections on engine performance and emissions. The results show that multiple pulsed injections can be used to significantly reduce both soot and NO x simultaneously in the engine. In addition, when combined with exhaust gas recirculation to further lower NO x, pulsed injections are found to be still very effective at reducing soot. The intake flow CFD modeling results show that the details of the intake flow process influence the engine performance. Comparisons with the measured engine cylinder pressure, heat release, soot and NO x emission data, and the combustion visualization flame images show that the CFD model results are generally in good agreement with the experiments. In particular, the model is able to correctly predict the soot—NO x trade-off trend as a function of injection timing. However, further work is needed to improve the accuracy of predictions of combustion with late injection, and to assess the effect of intake flows on emissions.