Corrosion inhibitors (CIs) have been used for years to protect the supply and distribution hardware used for transportation of fuel from refineries and to buffer the potential organic acids present in an ethanol blended fuel to enhance storage stability. The impact of these inhibitors on spark-ignition engine fuel systems, specifically intake valve deposits, is known and presented in open literature. However, the relationship of the corrosion inhibitors to the powertrain intake valve deposit performance is not understood. This paper has two purposes: to present and discuss a second market place survey of corrosion inhibitors and how they vary in concentration in the final blended fuel, specifically E85 (Ethanol Fuel Blends); and, to show how the variation in the concentrations of the components of the CIs impacts the operation and performance of vehicles, specifically, the effects on intake valve deposit formation.
The paper presents the development of a novel approach to the solution of detailed chemistry in internal combustion engine simulations, which relies on the analytical computation of the ordinary differential equations (ODE) system Jacobian matrix in sparse form. Arbitrary reaction behaviors in either Arrhenius, third-body or fall-off formulations can be considered, and thermodynamic gas-phase mixture properties are evaluated according to the well-established 7-coefficient JANAF polynomial form. The current work presents a full validation of the new chemistry solver when coupled to the KIVA-4 code, through modeling of a single cylinder Caterpillar 3401 heavy-duty engine, running in two-stage combustion mode.
The three-dimensional KIVA code has been used to study the effects of injection pressure and split injections on diesel engine performance and soot and NOx emissions. The code has been updated with state-of-the-art submodels including: a wave breakup atomization model, drop drag with drop distortion, spray/wall interaction with sliding, rebounding, and breaking-up drops, multistep kinetics ignition and laminar-turbulent characteristic time combustion, wall heat transfer with unsteadiness and compressibility, Zeldovich NOx formation, and soot formation with Nagle Strickland-Constable oxidation. The computational results are compared with experimental data from a single-cylinder Caterpillar research engine equipped with a high-pressure, electronically-controlled fuel injection system, a full-dilution tunnel for soot measurements, and gaseous emissions instrumentation.
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.
The study of combustion in direct injection Diesel engines demands detailed understanding of the behavior of the injection. Understanding the injection involves characterizing the distribution of fuel particle sizes throughout the spray. This work studied the size distributions of sprays from commercial Diesel injectors under a series of conditions. A diffraction-based diagnostic obtained maps of local fuel droplet size information over the full spray field. Most quantitative techniques currently used in spray research provide quantitative time-ranging data at a single point in the spray field. Spatially resolved information proves more useful in studying transient sprays. The spatially resolved maps of particle size obtained in this experiment showed the reliability of the diagnostic, exhibited the transience of the fine structure of these sprays, and demonstrated the evolution of the sprays with time.
Computational simulations of the spray combustion and emissions formation processes in a heavy-duty DI diesel engine and in a small-bore DI diesel engine with a complicated injection schedule were performed by using the modified KIVA3V, rel. 2 code. Some initial parameter sets varying engine operating conditions, such as injection pressure, injector nozzle diameter, EGR load, were examined in order to evaluate their effects on the engine performance. Full-scale combustion chamber representations on 360-deg, Cartesian and polar, multiblock meshes with a different number of sprays have been used in the modelling unlike the conventional approach based on polar sector meshes covering the region around one fuel spray. The spray combustion phenomena were simulated using the detailed chemical mechanism for diesel fuel surrogate (69 species and 306 reactions).
A global optimization method has been developed for an engine simulation code and utilized in the search of optimal fuel injection strategies. This method uses a Lagrange interpolation function which interpolates engine output data generated at the vertices and the intermediate points of the input parameters. This interpolation function is then used to find a global minimum over the entire parameter set, which in turn becomes the starting point of a CFD-based optimization. The CFD optimization is based on a steepest descent method with an adaptive cost function, where the line searches are performed with a fast-converging backtracking algorithm. The adaptive cost function is based on the penalty method, where the penalty coefficient is increased after every line search. The parameter space is normalized and, thus, the optimization occurs over the unit cube in higher-dimensional space.
Engine-out CO emission and fuel conversion efficiency were measured in a highly-dilute, low-temperature diesel combustion regime over a swirl ratio range of 1.44-7.12 and a wide range of injection timing. At fixed injection timing, an optimal swirl ratio for minimum CO emission and fuel consumption was found. At fixed swirl ratio, CO emission and fuel consumption generally decreased as injection timing was advanced. Moreover, a sudden decrease in CO emission was observed at early injection timings. Multi-dimensional numerical simulations, pressure-based measurements of ignition delay and apparent heat release, estimates of peak flame temperature, imaging of natural combustion luminosity and spray/wall interactions, and Laser Doppler Velocimeter (LDV) measurements of in-cylinder turbulence levels are employed to clarify the sources of the observed behavior.
Diesel engine in-cylinder combustion processes have been studied using computational models with particular attention to spray development, vaporization, fuel/air mixture formation and combustion. A thermodynamic zero-dimensional cycle analysis program was used to determine initial conditions for the multidimensional calculations. A modified version of the time-dependent, three-dimensional computational fluid dynamics code KIVA-II was used for the computations, with a detailed treatment for the spray calculations and a simplified model for combustion. The calculations were used to obtain an understanding of the potential predictive capabilities of the models. It was found that there is a strong sensitivity of the results to numerical grid resolution. With proper grid resolution, the calculations were found to reproduce experimental data for non- vaporizing and vaporizing sprays. However, for vaporizing sprays with combustion, extremely fine grids are needed.
A study of partially premixed combustion (PPC) with non-oxygenated 91 pump octane number1 (PON) commercially available gasoline was performed using a heavy-duty (HD) compression-ignition (CI) 2.44 l Caterpillar 3401E single-cylinder oil test engine (SCOTE). The experimental conditions selected were a net indicated mean effective pressure (IMEP) of 11.5 bar, an engine speed of 1300 rev/min, an intake temperature of 40°C with intake and exhaust pressures of 200 and 207 kPa, respectively. The baseline case for all studies presented had 0% exhaust gas recirculation (EGR), used a dual injection strategy a -137 deg ATDC pilot SOI and a -6 deg ATDC main start-of-injection (SOI) timing with a 30/70% pilot/main fuel split for a total of 5.3 kg/h fueling (equating to approximately 50% load). Combustion and emissions characteristics were explored relative to the baseline case by sweeping main and pilot SOI timings, injection split fuel percentage, intake pressure, load and EGR levels.
Transient engine operations are modeled and simulated with a 1-D code (GT Power) using heat release and emission data computed by a 3-D CFD code (Kiva3). During each iteration step of a transient engine simulation, the 1-D code utilizes the 3-D data to interpolate the values for heat release and emissions. The 3-D CFD computations were performed for the compression and combustion stroke of strategically chosen engine operating points considering engine speed, torque and excess air. The 3-D inlet conditions were obtained from the 1-D code, which utilized 3-D heat release data from the previous 1-D unsteady computations. In most cases, only two different sets of 3-D input data are needed to interpolate the transient phase between two engine operating points. This keeps the computation time at a reasonable level. The results are demonstrated on the load response of a generator which is driven by a medium-speed diesel engine.
Intake port and cylinder flow have been modeled for a dual intake valve diesel engine. A block structured grid was used to represent the complex geometry of the intake port, valves, and cylinder. The calculations were made using a pre-release version of the KIVA-3 code developed at Los Alamos National Laboratories. Both steady flow-bench and unsteady intake calculations were made. In the flow bench configuration, the valves were stationary in a fully open position and pressure boundary conditions were implemented at the domain inlet and outlet. Detailed structure of the in-cylinder flow field set up by the intake flow was studied. Three dimensional particle trace streamlines reveal a complex flow structure that is not readily described by global parameters such as swirl or tumble. Streamlines constrained to lie in planes normal to the cylinder axis show dual vortical structures, which originated at the valves, merging into a single structure downstream.
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.
This research focused on the effects of split injection on fuel spray behavior in a diesel environment. It was done in a special designed engine-fed combustion chamber (swirl ratio of 5) with full field optical access through a quartz window. The simulated engine combustion chamber used a special backwards spraying injector (105°). The electronically controlled injector could control the size and position of it's two injections. Both injections were through the same nozzle and it produced very rapid injections (1.5 ms) with a maximum injection pressure of 130 MPa. Experimental data included: rate of injection, injector pressure, spray plume images, tip penetration, liquid and vapor fuel distributions, combustion pressure, and rate of pressure rise. From 105° forward scatter images, tip penetration was observed to be very rapid and reached a plateau at 25 mm.
An experimental investigation of the spectral characteristics of turbulent flow in a scale model of a high pressure diesel fuel injector nozzle hole has been conducted. Instantaneous velocity measurements were made in a 50X transparent model of one hole of an injector nozzle using an Aerometrics Phase/Doppler Particle Analyzer (PDPA) in the velocity mode. Turbulence spectra were calculated from the velocity data using the Lomb-Scargle method. Injector hole length to diameter ratio (L/D) values of 1.3, 2.4, 4.9, and 7.7 and inlet radius to diameter ratio (R/D) values of approximately 0 and 0.3 were investigated. Results were obtained for a steady flow average Reynolds number of 10,500, which is analogous to a fuel injection velocity of 320 m/s and a sac pressure of approximately 67 MPa (10,000 psi). Turbulence time frequency spectra were obtained for significant locations in each geometry, in order to determine how geometry affects the development of the turbulent spectra.
This Paper introduces a modular, flexible and user-friendly dynamic powertrain model of the US Army's High Mobility Multi-Wheeled Vehicle (HMMWV). It includes the DDC 6.5L diesel engine, Hydra-matic 4L80-E automatic transmission, Torsen differentials, transfer case, and flexible drive and axle shafts. This model is used in a case study on transmission optimization design to demonstrate an application of the model. This study shows how combined optimization of the transmission hardware (clutch capacity) and control strategy (shift time) can be explored, and how the models can help the designer understand dynamic interactions as well as provide useful design guidance early in the system design phase.
An experimental study of luminous combustion in a modern diesel engine was performed to investigate the effect of injection parameters on NOX and soot formation via flame temperature and soot KL factor measurements. The two-color technique was applied to 2-D soot luminosity images and area-averaged soot radiation signals to obtain spatially and temporally resolved flame temperature and soot KL factor. The imaging system used for this study was based on a wide-angle endoscope that was mounted in the cylinder head and allowed different views of the combustion chamber. The experiments were carried out on a single-cylinder 2.4 liter D.I. diesel engine equipped with an electronically controlled common-rail injection system. Operating conditions were 1600 rpm and 75% load. The two-color results confirm that retarding the injection timing causes lower flame temperatures and NOX emissions but increased soot formation, independent of injection strategy.
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.
Vapor concentration measurements were performed for two unit injectors typically found in small- and medium-bore applications under evaporating conditions similar to those experienced in Diesel engines. Ambient gas temperatures of 800 and 1000 K and an ambient density of 15 kg/m3 were investigated using a constant volume combustion-type spray chamber. The exciplex laserinduced fluorescence technique with TMPD/naphthalene doped into the fuel was used to quantitatively determine the vapor-phase concentration and liquid-phase extent. The vapor-phase concentration was quantified using a previously developed method that includes corrections for the temperature dependence of the TMPD fluorescence, laser sheet absorption, and the laser sheet intensity profile. The effect of increasing ambient temperature (1000 vs. 800 K) was significant on intact liquid length, and on the spray-spreading angle in the early portion of the injection period.