Application of Hyperbolic Tangent Approximation Model to Gasoline Direct Injection Engine Simulation

The improved fuel economy and low pollutant emissions are highly demanded for internal combustion engines. Gasoline Direct Injection (GDI) engine is the one of promising devices for highly efficient engine. However, GDI engines generally tend to emit more Particulate Matter (PM) than Port Fuel Injection (PFI) engine because the fuel sprayed from the injector can easily attach to the wall, which is the major origin of PM. Therefore, the precise analysis of the fuel/air mixture formation and the prediction of emissions are required. From the view of industrial use, Computational Fluid Dynamics (CFD) becomes a necessary tool for the various analyses including the fuel/air mixture formation, spray attachment on the cylinder wall, the in-cylinder turbulence formation, the combustion and emission etc. In our previous study, the flow and spray simulation in internal combustion engine has been conducted using OpenFOAM®, the open-source CFD toolbox. Since the engine involves the dynamic motion such as valve and piston, the morphing and mapping approach was employed. Furthermore, by virtue of open-source code, we have developed the methodology of the hybrid simulation from the internal nozzle flow to the fuel/air mixture in order to take into account detailed breakup process nearby injector nozzle. We expand the above research to the combustion simulation. For the combustion model, the Hyperbolic Tangent Approximation (HTA) model is adopted. The HTA model has a simple form of equation and one can easily implement; moreover, the HTA model has the following features: 1. capability of both laminar and turbulent flow, 2. the clearness of analytical derivation based on the functional approximation of the reaction progress variable distribution in a one-dimensional laminar flame. In the current study, the premixed flame is studied on a gasoline combustion engine. The simulations for in-cylinder engine are conducted with different Air/Fuel (A/F) ratio conditions, and the results are compared with the experimental results. The in-cylinder pressure agrees well with experimental results and the validity of the current methodology is confirmed.

Methods to Improve Combustion Stability, Efficiency, and Power Density of a Small, Port-Injected, Spark-Ignited, Two-Stroke Natural Gas Engine

Two-stroke engines are often used for their low cost, simplicity, and power density. However, these engines suffer efficiency penalties due to fuel short-circuiting. Increasing power density has previously been an area of focus for performance two-stroke engines — such as in dirt bikes. Smaller-displacement engines have also been used to power remote controlled cars, boats, and aircraft. These engines typically rely on gasoline or higher-octane liquid fuels. However, natural gas is an inherently knock-resistant fuel and small natural gas engines and generators could see increased market penetration. Power generators typically operate at a fixed frequency with varied load, which can take advantage of intake and exhaust system tuning. In addition, stationary engines may not be subject to size restrictions of optimal intake and exhaust systems. This paper examines methods to improve combustion stability, efficiency, and power density of a 29cc air-cooled two-stroke engine converted to operate on natural gas. Initial conversion showed significant penalties on delivery ratio, which lowered power density and efficiency. To overcome these issues a tuned intake pipe, two exhaust resonators, and a combustion dome were designed and tested. The engine was operated at 5400 RPM and fueling was adjusted to yield maximum brake-torque (MBT). All tests were conducted under wide-open throttle conditions. The intake and exhaust systems were designed based on Helmholtz resonance theory and empirical data. The engine utilized a two-piece cylinder head with removable combustion dome. The combustion dome was modified for optimal compression ratio while decreasing squish area and volume. With all designs incorporated, power increased from 0.22 kW to 1.07 kW — a factor of 4.86. Efficiency also increased from 7% to 12%. In addition to these performance gains, the coefficient of variation (COV) of indicated mean effective pressure (IMEP) decreased from just above 11% to less than 4%.

Parallel Multi-Cycle LES of an Optical Pent-Roof DISI Engine Under Motored Operating Conditions

The use of Large-eddy Simulations (LES) has increased due to their ability to resolve the turbulent fluctuations of engine flows and capture the resulting cycle-to-cycle variability. One drawback of LES, however, is the requirement to run multiple engine cycles to obtain the necessary cycle statistics for full validation. The standard method to obtain the cycles by running a single simulation through many engine cycles sequentially can take a long time to complete. Recently, a new strategy has been proposed by our research group to reduce the amount of time necessary to simulate the many engine cycles by running individual engine cycle simulations in parallel. With modern large computing systems this has the potential to reduce the amount of time necessary for a full set of simulated engine cycles to finish by up to an order of magnitude. In this paper, the Parallel Perturbation Methodology (PPM) is used to simulate up to 35 engine cycles of an optically accessible, pent-roof Direct-injection Spark-ignition (DISI) engine at two different motored engine operating conditions, one throttled and one un-throttled. Comparisons are made against corresponding sequential-cycle simulations to verify the similarity of results using either methodology. Mean results from the PPM approach are very similar to sequential-cycle results with less than 0.5% difference in pressure and a magnitude structure index (MSI) of 0.95. Differences in cycle-to-cycle variability (CCV) predictions are larger, but close to the statistical uncertainty in the measurement for the number of cycles simulated. PPM LES results were also compared against experimental data. Mean quantities such as pressure or mean velocities were typically matched to within 5–10%. Pressure CCVs were under-predicted, mostly due to the lack of any perturbations in the pressure boundary conditions between cycles. Velocity CCVs for the simulations had the same average magnitude as experiments, but the experimental data showed greater spatial variation in the root-mean-square (RMS). Conversely, circular standard deviation results showed greater repeatability of the flow directionality and swirl vortex positioning than the simulations.

Optimization of Mixture Formation of Diesel Fuel in a Small CI Engine: The Effect of Water (H2O) Injection Into Intake Port

The objective of this study is to investigate the effect of water injection into intake port on the performance of small CI engine. The ECFM-3Z model was applied for the combustion analysis model, and the amount of injected water were varied 10%, 20% and 30% of injected fuel mass. The results of this work were compared in terms of cylinder pressure, rate of heat release (ROHR), and the ISNO and soot emissions. It was found that the cylinder pressure was decreased from 1.2% to 9.2% when the amount of injected water was increased from 10% to 30%. In the results, NO emission significantly decreased from about 24% to about 85% when the amount of injected water increased due to the specific heat and latent heat of water. Considering the test results, the best conditions for the simultaneous reduction of NO and soot is the BTDC 05deg of injection timing and 30% of water injection mass. It can be expected the best IMEP and ISFC characteristics.

Seizure Improved Lead-Free Electroplated Bearing Overlay System for Heavy Duty Truck and Off-Highway Applications

The move to lead-free bearing materials is well known and upcoming legislation, such as the Restriction of Hazardous Substances (RoHS), is increasing the drive to extend this trend towards heavy duty diesel truck and off-highway applications. During the development of lead-free systems, new electroplated overlays and bronze-based substrates have been developed by various suppliers, but little attention has been given to the interlayer or diffusion barrier between the overlay and substrate materials. This interlayer is particularly necessary for tin-based solutions as it prevents the rapid diffusion of overlay species into the bronze substrate. The present development focuses on improving this often overlooked element in the system and provides a further robustness that could even be adapted to lead-based systems where increased performance is required. The incorporation of hexagonal boron nitride as a solid lubricant in the nickel interlayer changes dramatically the interlayer properties and provides more typical bearing-like behavior for seizure resistance scuff performance compared to nickel alone. The paper details findings of respective rig tests as well as an actual engine test supporting the change in material characteristics and the associated improvement in seizure resistance.

Development of a Numerical Model for Ignition Phenomena in a Micro Pilot Ignited Dual Fuel Engine With External Mixture Formation

In this paper, a numerical investigation of the ignition process of dual fuel engines is presented. Optical measurements revealed that a homogeneous natural gas charge ignited by a small diesel pilot comprises the combustion phenomena of compression ignition of the pilot fuel as well as premixed flame propagation. The 3-Zones Extended Coherent Flame Model (ECFM3Z) was selected, since it can treat auto-ignition, pre-mixed flame propagation and diffusion flame aspects. Usually combustion models in multi-dimensional computational fluid dynamics (CFD) software packages are designed to handle only one reactive species representing the fuel concentration. In the context of the ECFM3Z model the concept of a multi-component fuel is applied to dual fuel operation. Since the available ignition models were not able to accurately describe the ignition characteristics of the investigated setup, a new dual fuel auto-ignition model was developed. Ignition delay times of the fuel blend are tabulated using a detailed reaction mechanism for n-heptane. Thereby, the local progress of pre-ignition reactions in the CFD simulation can be calculated. The ignition model is validated against experiments conducted with a periodically chargeable constant volume combustion chamber. The proposed model is capable to reproduce the ignition delay as well as the location of the flame kernels. The CFD simulations show the effect of temperature stratification and variations in the injection pressure on the apparent ignition delay of the micro pilot.

1.25 L Turbocharged Diesel for Demanding Non-Road Applications

A design process was defined and implemented for the rapid development of purpose-built, heavy-fueled engines using modern CAE tools. The first exercise of the process was the clean sheet design of the 1.25 L, three-cylinder, turbocharged AMD45 diesel engine. The goal of the AMD45 development program was to create an engine with the power density of an automotive engine and the durability of an industrial/military diesel engine. The AMD45 engine was designed to withstand 8000 hours of operation at 4500 RPM and 45 kW output, while weighing less than 100 kg. Using a small design team, the total development time to a working prototype was less than 15 months. Following the design phase, the AMD45 was fabricated and assembled for first prototype testing. The minimum-material-added design approach resulted in a lightweight engine with a dry weight 89 kg for the basic engine with fuel system. At 4500 RPM and an intake manifold pressure of 2.2 bar abs., the AMD45 produced 62 kW with a peak brake fuel-conversion efficiency greater than 34%. Predictions of brake power and efficiency from the design phase matched to within 5% of experimental values. When the engine is detuned to 56 kW maximum power, the use of multi-pulse injection and boost pressure control allowed the AMD45 to achieve steady state emissions (as measured over the ISO 8178 C1 test cycle) of CO and NOx+NMHC that met the EPA Tier 4 Non-road standard without exhaust after-treatment, with the exception of idle testing. PM emissions were also measured, and a sulfur-tolerant diesel particulate filter has been designed for PM after-treatment.

The Effects of Injection Timing and Injected Fuel Mass on Local Charge Conditions and Emissions for Gasoline Direct Injection Engines

Increased Particulate Matter (PM) emissions from Gasoline Direct Injection (GDI) engines compared to conventional Port Fuel Injection (PFI) engines have been raising concerns because of the PM’s detrimental health effects and the stringent emissions regulations. One of the widely accepted hypotheses is that local rich pockets inside the combustion chamber are the primary reason for the increased PM emissions. In this paper, we investigate the effects of injection strategies on the charge composition and local thermodynamic conditions of a light duty GDI engine, and determine their impact on PM emissions. The operation of a 1.6L GDI engine is simulated using a 3-D Computational Fluid Dynamics (CFD) code. Combustion characteristics of a 3-component gasoline surrogate (n-heptane/iso-octane/toluene) are analyzed and the effects of injection timing (300° vs 240° vs 180° BTDC) and injected fuel mass (globally stoichiometric vs fuel rich) are explored at 2000 rpm, 9.5 bar BMEP condition, focusing on the homogeneity of the charge and the formation of the gaseous species that are soot precursors. The results indicate that when the physical time for air/fuel mixing is not long enough, fuel-rich pockets are present until combustion occurs, where high concentrations of soot precursors are found, such as acetylene and pyrene. In addition, simulation results indicate that the location of wetted surface as well as the in-cylinder flow structure induced by the fuel jet hitting the piston bowl is significantly influenced by varying the injection timing, which affects subsequent air/fuel mixing. When the injected fuel mass is increased, the equivalence ratio distribution inside the combustion chamber shifts toward fuel-rich side, generating more mixtures with Φ > 1.5, where formation of acetylene and pyrene are favored.

Poison Build-up and Performance Degradation of an Oxidation Catalyst in 2-Stroke Natural Gas Engine Exhaust

Due to current and future exhaust emissions regulations, oxidation catalysts are increasingly being added to the exhaust streams of large-bore, 2-stroke, natural gas engines. Such catalysts have been found to have a limited operational lifetime, primarily due to chemical (i.e. catalyst poisoning) and mechanical fouling resulting from the carry-over of lubrication oil from the cylinders. It is critical for users and catalyst developers to understand the nature and rate of catalyst deactivation under these circumstances. This study examines the degradation of an exhaust oxidation catalyst on a large-bore, 2-stroke, lean-burn, natural gas field engine over the course of 2 years. Specifically this work examines the process by which the catalyst was aged and tested and presents a timeline of catalyst degradation under commercially relevant circumstances. The catalyst was aged in the field for 2 month intervals in the exhaust slipstream of a GMVH-12 engine and intermittently brought back to the Colorado State Engines and Energy Conversion Laboratory for both engine testing and catalyst surface analysis. Engine testing consisted of measuring catalyst reduction efficiency as a function of temperature as well as the determination of the light-off temperature for several exhaust components. The catalyst surface was analyzed via SEM/EDS and XPS techniques to examine the location and rate of poison deposition. After 2 years on-line the catalyst light-off temperature had increased ∼55°F (31°C) and ∼34 wt% poisons (S, P, Zn) were built up on the catalyst surface, both of which represent significant catalyst deactivation.