The advantages of hydrogen fueled internal combustion engines are well known, certainly concerning the ultra low noxious emissions (only NO x is to be considered). Disadvantages are the backfire phenomenon and the gaseous state of hydrogen at atmospheric conditions. A complete control of the mixture formation is necessary and therefore a test engine with sequential port injection was chosen. The tests are carried out on a single cylinder CFR engine with the intention to use the results to optimize a 6 and 8 cylinder engine with multipoint injection. Different positions of the injector against the intake air duct are examined (represented as different junctions). A numerical simulation CFD code (FLUENT) is used under “stationary” conditions (continuous injection) for all geometries and under “real” conditions (sequential injection) for one situation. For each of the geometries the influences of the start of injection, the air/fuel equivalence ratio, injection pressure and ignition timing on the power output and efficiency of the engine are analyzed. A comparison and discussion is given for all results. It is clearly shown that the start of injection for a certain engine speed and inlet geometry influences the volumetric efficiency and thus the power output of the engine due to the interaction between the injected hydrogen and the inlet pressure waves. Furthermore, the small influence of the injection pressure and the contradictory benefits of the different junctions between power output and fuel efficiency are measured. With retarded injection, so that cool air decreases the temperature of the “hot-spots” in the combustion chamber before the fuel is injected, backfire safe operation is possible.

Porous media (PM) has interesting advantages in compared with free flame combustion due to the higher burning rates, the increased power range, the extension of the lean flammability limits, and the low emissions of pollutants. Future clean internal combustion (IC) engines should have had minimum emissions level (for both gaseous and particulate matter) under possible lowest fuel consumption permitted in a wide range of speed, loads and having good transient response. These parameters strongly depend on mixture formation and combustion processes which are difficult to be controlled in a conventional engine. This may be achieved by realization of homogeneous combustion process in engine. This paper deals with the simulation of direct injection IC engine equipped with a chemically inert PM, with cylindrical geometry to homogenize and stabilize the combustion of engine. A 3D numerical model for PM engine is presented in this study based on a modified version of the KIVA-3V code. Due to lack of any published data for PM engines, numerical results of thermal and combustion wave propagation in a porous medium are compared with experimental data of lean methane-air mixture under filtration in packed bed and very good agreement is seen. For PM engine simulation methane as a fuel is injected directly inside hot PM that is assumed, mounted in cylinder head. Lean mixture is formed and volumetric combustion occurs in PM and in-cylinder. Mixture formation, pressure and temperature distribution in both phases of PM and in-cylinder fluid with the production of pollutants CO and NO and also effects of injection time in the closed part of the cycle are studied.

Due to the vast resources of natural gas (NG), it has emerged as an alternative fuel for SI internal combustion engines in recent years. The need to have better fuel economy and less emission especially that of greenhouse gases has resulted in development of NG fueled engines. Direct injection of natural gas into the cylinder of SI internal combustion engines has shown great potential for improvement of performance and reduction of engine emissions especially CO2 and PM. Direct injection of NG into the cylinder of SI engines is rather new thus the flow field phenomena and suitable configuration of injector and combustion chamber geometry has not been investigated completely. In this study a numerical model has been developed in AVL FIRE software to perform investigation of direct natural gas injection into the cylinder of spark ignition internal combustion engines. In this regard, two main parts have been taken into consideration aiming to convert an MPFI gasoline engine to direct injection NG engine. In the first part of study multidimensional numerical simulation of transient injection process, mixing and flow field have been performed via different validation cases in order to assure the numerical model validity of results. Adaption of such a modeling was found to be a challenging task because of required computational effort and numerical instabilities. In all cases present results were found to have excellent agreement with experimental and numerical results from literature. In the second part, using the moving mesh capability, the validated model has been applied to methane injection into the cylinder of a direct injection engine. Five different piston head shapes have been taken into consideration in investigations. An inwardly opening multi-hole injector has been adapted to all cases. The injector location has been set to be centrally mounted. The effects of combustion chamber geometry have been studied on mixing of air-fuel inside cylinder via quantitative and qualitative representation of results. Based on the results, suitable geometrical configuration for a NG DI engine has been discussed.

In this paper, a new hydraulic variable valve actuation system is proposed. Using this system, the engine valve opening and closing timings and lift are flexibly controlled with two rotary spool valves actuated by the engine crankshaft. High degree of flexibility with less control complexity and high repeatability are the advantages of this system over other camless valvetrains; however, in this system, there is a trade-off between its robustness and power consumption. A numerical model of the system is developed to study the system functionality at different operating conditions. To validate the developed model, the simulation results for a random operating condition are compared with those from the experiments. A sensitivity analysis is done to study the effects of variations in different design parameters on system robustness and power consumption. The results prove that increasing engine valve return-spring stiffness and actuator piston area will reduce the mechanism sensitivity to engine cycle-to-cycle variations; however, this results in poor energy efficiency. Therefore, a neat energy recovery strategy is developed to recuperate a portion of the energy used to compress the engine valve return-spring during valve opening interval. The results show that more than 90% of the extra energy wasted for the sake of system robustness could be regenerated through the proposed energy recovery system.

This work deals with the analysis of the performance and emissions of ethanol HCCI/PSCCI engines by means of a Dynamic Adaptive Chemistry (DAC) technique. The implementation of such a technique provides a reduction of the computational cost of the simulations without compromising the reliability of the results. Very accurate results, in terms of pressure and heat release rate profiles and CO, CO 2 and UHC emissions, are obtained with ethanol as the only species for the DRGEP graph search both with the charge uniformly distributed in the combustion chamber and by directly injecting liquid fuel in the same chamber. The global speed up of DAC simulations is twice with respect to a full mechanism which consists of 57 species and 288 reactions and a further increase is expected when DAC is compared to very detailed kinetics.

Lean large-bore natural gas engines are usually equipped with gas-scavenged prechambers. After ignition and during combustion in the prechamber hot reacting jets penetrate the main chamber and provide much higher ignition energies than electric spark plugs. Although prechambers stabilize combustion, limitations of the concept are observed at very lean main chamber mixtures and large cylinder diameters, which appear as cycle-to-cycle variations of heat release and pressure. At the Thermodynamics Institute of the Technical University of Munich cycle-to-cycle variations are investigated in an unique periodically chargeable high pressure combustion cell with full optical access to the entire main chamber. Recently, the influence of the ignition timing, the amount of scavenge-gas of the prechamber and the cross section of the prechamber exit orifices on cycle-to-cycle variations have been studied. From the pressure traces characteristic parameters of the combustion process like the ignition probability, the ignition delay and the rate of the pressure rise have been derived. By analysing the emission of OH*-chemiluminescence in terms of reacting area and light emission and on the basis of numerical simulations information on the source of cycle-to-cycle variations is obtained. Finally it is shown that cycle-to-cycle variations can be reduced remarkably by appropriate selection and combination of prechamber geometry and operating parameters.

In the last few years, a significant research effort has been made for developing and enhancing Direct Injection (DI) for compressed natural gas (CNG) engines. Several research projects have been promoted by the European Community (EC) in this field with the objective of finding new solutions for the automotive market and also of encouraging a fruitful knowledge exchange among car manufacturers, suppliers and technical universities. This paper concerns part of the research activity that has been carried out by the Politecnico di Torino, AVL List GmbH and Siemens AG within the EC VII Framework Program (FP) InGAS Collaborative Project (CP), aimed at optimizing the control phase of a new injector for CNG direct injection, paying specific attention to its behavior at small injected-fuel amounts, i.e., small energizing times. The CNG injector which was developed within the research project proved to be suitable to be used in a DI SI engine, featuring a pent-roof combustion chamber head and a bowl in piston, with reference to both homogeneous and stratified charge formation. Fuel flow measurements made by AVL on the four-cylinder engine revealed a good linearity between injection duration and fuel mass-flow rate for injection durations above a reference value. In order to improve the injector characterization at short injection durations, an experimental and numerical activity was designed. More specifically, a multidimensional CFD model of the actual injector geometry was built by Politecnico di Torino, and purposely-designed simulation cases were carried out, in which the needle-lift time-history was defined on the basis of experimental measurements made by Siemens. The numerical model was validated on the basis of experimental data concerning the total injected-fuel amount under different conditions. Then, the model was applied in order to evaluate the dynamic flow characteristic by taking also the inner geometry of the injector valve group into account, so as to establish a correlation to the needle lift measurements done by Siemens for injector characterization. In the paper this dynamic behavior of the injector is analyzed, under actual operating conditions, and its impact on the nozzle injection capability is discussed. The simulation results did not show significant oscillations of the stagnation pressure upstream of the nozzle throat section, and thus the resultant mass-flow rate profile is almost proportional to the needle-lift one. As a consequence, in order to characterize the injector flow behavior in the nonlinear region (short injection duration), the measurement of needle lift is sufficient.

Nowadays, many urban buses for public transportation are fuelled by compressed natural gas (CNG), due to its potential for energy saving and pollutant reduction, with specific reference to particulate matter emissions. However, turbocharging is required to recover the gaseous-fuel related power gap with respect to more traditional engines running on liquid fuels. Therefore, turbolag reduction is fundamental to achieve high performance during engine transients. Significant support for the study of turbocharged CNG engines and guidelines for the turbomatching process can be provided by 1D numerical simulation tools. In this paper, the topic of turbolag reduction is analyzed, and different strategies, namely, Early-Exhaust Valve Opening-Variable Valve Actuation (E-EVO-VVA) and spark timing control for combustion retard (ComR), are analyzed by means of a specifically developed and calibrated GT-POWER ® engine model. Tip-in maneuvers in which the engine was coupled to a torque hydraulic converter under stall conditions were investigated, so as to reproduce a typical load transient condition for an urban bus accelerating from engine idle. The best improvement of turbolag was obtained by combining E-EVO-VVA and ComR, with a reduction of turbolag ranging from 60% to 70%. When a limit on the incylinder pressure is introduced, in order to prevent excessive exhaust valve mechanical stresses, the higher achievable reduction in turbolag was found to be between 35% and 45%.

Heat flux measurements were performed in an air-cooled utility engine using a fast-response coaxial-type surface thermocouple. The surface heat flux was calculated using both analytical and numerical models. The heat flux was found to be a strong function of engine load. The peak heat flux and initial heat flux rise rate increase with engine load. The measured heat flux data were used to estimate a global heat transfer rate, and this was compared with the heat transfer rate calculated by a single-zone heat release analysis. The measured values of heat transfer were higher than the calculated values largely because of the lack of spatial averaging. The high load data showed an unexplainable negative heat flux during the expansion stroke while the gas temperature was still high. A 1D and 2D finite difference numerical model utilizing an adaptive timestep Crank-Nicholson (CN) integration routine was developed to investigate the surface temperature measurement. Applying the measured surface temperature profile to the 1D model, the resultant surface heat flux showed excellent agreement with the analytical inversion solution and captured the reversal of the energy flow back into the cylinder during the expansion stroke. The 2D numerical model was developed to observe transient lateral conduction effects within the probe and incorporated the various materials used in the construction and assembly of the heat flux sensor. The resulting average heat flux profile for the test case is shown to be slightly higher in peak and longer in duration when compared with the results from the 1D analytical inversion, and this is attributed to contributions from the high thermal diffusivity constituents in the sensor. Furthermore, the negative heat flux at high load was not eliminated suggesting that factors other than lateral conduction may be affecting the measurement accuracy.

During the last years, the integration of computational CFD tools in the internal combustion (IC) engine design process has continuously been increased, allowing to save time and cost as the need of experimental prototypes has diminished. Numerical analyses of IC engine flows are rather complex from both the conceptual and operational sides. In fact, such flows involve a variety of unsteady phenomena, and the right balance between numerical solution accuracy and computational cost should be always reached. The present paper is focused on computational modeling of natural gas (NG) direct injection (DI) processes from a poppet-valve injector into a bowl-shaped combustion chamber. At high injection pressures, the efflux of gas from the injector and the mixture formation processes include compressible and turbulent flow features, such as rarefaction waves and shock formation, which are difficult to be accurately captured by the numerical simulation, particularly when combustion chamber geometry is complex and piston and intake/exhaust valve grids are moving. A three-dimensional moving grid model of the combustion engine chamber, originally developed by the authors, was enhanced by increasing the accuracy in the sonic section proximity of the critical valve seat nozzle, in order to precisely capture the expansion dynamics the methane undergoes inside the injector and immediately downstream from it. The enhanced numerical model was validated by comparing numerical results to Schlieren experimental images for nitrogen injection into a constant-volume bomb. Then, numerical studies were carried out in order to characterize the fuel jet properties and the evolution of mixture-formation for a centrally-mounted injector configuration in both cases of a pancake test chamber and the real-shaped engine chamber. Finally, the fluid properties computed by the model in the throat-section of the critical nozzle were taken as reference data for developing a new effective ‘virtual injector’ model, which allows the designer to remove the whole computational domain upstream from the sonic section of the nozzle, keeping the flow properties practically unchanged. The outcomes of such a virtual injector model were shown to be in very good agreement with the results of the enhanced complete injector model, confirming the reliability of the proposed novel approach.

Nowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields. Although hardware and numerical model improvements, the mesh generation remains one of the key points for a successful CFD simulation. Mesh quality is influenced by the adopted mesh generator tool and, after all, by the designer’s experience and it becomes very important when moving meshes are required. In fact, mesh skewness, aspect ratio, and non-orthogonality have to be controlled during the deforming process since their wrong evolution could produce an unphysical behavior of the computed flow field. Mesh motion could be performed by different strategies: dynamic smoothing operation and dynamic re-meshing operation, are, today, two of the mainly used approaches. All of them can be combined to guarantee the correct reproduction of motion profile and a good mesh quality level. In this context, the authors have implemented a moving mesh methodology in the Open Source CFD code OpenFOAM®. A multiple number of meshes is used to cover the whole simulation period, and the grid point motion is accommodated by an automatic mesh motion techinque with polyhedral cell support. The Laplace equation is chosen to govern mesh motion. This guarantees that an initial valid mesh remains valid for arbitrary boundary motion. Mesh to mesh interpolation is performed by using a cell based, distance weighted interpolation technique. The proposed approach was tested on a real IC-engine geometry. In particular, the mesh quality evolution during motion, the numerical results and the computational costs were evaluated.

This paper presents results from Phase 2 of the development of an Active Air Control (AAC) system to balance air flow into each cylinder of a turbocharged engine system, a PRCI-funded emissions reduction project. Imbalance in air flow creates a discontinuity in trapped equivalence ratio from cylinder to cylinder. Trapped equivalence ratio is directly proportional to NO X production and a function of the fuel flow rate, air flow rate, and, in a two-stroke cycle engine, the scavenging efficiency. Only when these three characteristics are balanced cylinder to cylinder will the combustion and the NO X production in each cylinder be equal. The engine NO X production will be disproportionately high if even one cylinder operates less lean relative to the other cylinders. This paper reports on the testing of an AAC system on a two-cylinder air flow bench at the National Gas Machinery Laboratory at Kansas State University. The results from these tests were then used to further validate the comprehensive, variable geometry, multi-cylinder flow model referred to as the Charge Air Integrated Manifold Engine Numerical Simulation (CAIMENS). CAIMENS is a manifold flow model coupled with the T-RECS engine processor that uses an integrated set of fundamental principles to determine the crank angle-resolved pressure, temperature, burned and unburned mass fractions, and gas exchange rates for the cylinder. CAIMENS has been validated with data from the NGML multi-cylinder flow bench. This information has allowed the research team to (1) quantify the impact of air flow imbalance and (2) provide detailed information leading to the specification of the active air flow control system. The end point of this project is an AAC system that can, with some engineering effort, be applied to field engines.

A mathematical model for cylinder-piston system considering the coupling between dynamic behavior and tribological behavior is presented in this paper. The three-dimensional finite element method is used to compute the engine block vibrations. The lubrication of cylinder-piston pair was described by an average Reynolds equation considering the piston second-vibration and asperity contact of rough surface. The corresponding computing program developed can be used to calculate the engine block vibrations, the entire piston trajectory, the Piston slap forces, friction forces and oil film thickness etc. as functions of crank angle under engine running conditions. The numerical simulation results show that the coupling between engine block dynamical behavior and lubrication has big influence for the secondary motion of piston and the engine block vibration in cylinder-piston system. It is essential to consider the engine block vibration in the analysis of cylinder-piston tribology.

A numerical study on the investigation of spray evolution and liquid film formation within the combustion chamber of a current production automotive Gasoline Direct Injected (GDI) engine characterised by a swirl-type side mounted injector is presented. Particularly, the paper focuses on low-temperature cranking operation of the engine, when, in view of the high injected fuel amount and the strongly reduced fuel vaporisation, wall wetting becomes a critical issue and plays a fundamental role on the early combustion stages. In fact, under such conditions, fuel deposits around the spark plug region can affect the ignition process, and even prevent engine start-up. In order to properly investigate and understand the many involved phenomena, experimental visualisation of the full injection process by means of an optically accessible engine would be a very useful tool. Nevertheless, the application of such technique, far from being feasible from an industrial point of view, appears to be very difficult even in research laboratories, due to the relevant wall wetting at cranking conditions. A numerical program was therefore carried out in order to analyze in depth and investigate the wall/spray interaction and the subsequent fuel deposit distribution on the combustion chamber walls. The CFD model describing the spray conditions at the injector nozzle was previously implemented and validated against experimental evidence. Many different injection strategies were tested and results compared in terms of both fuel film characteristics and fuel/air mixture distribution within the combustion chamber. Low-temperature cranking conditions proved to be an open challenge for the in-cylinder numerical simulations, due to the simultaneous presence of many physical sub-models (spray evolution, droplet-droplet interaction, droplet-wall interaction, liquid-film) and the very low motored engine speed. Nevertheless, the use of a properly customized and validated numerical setup led to a good understanding of the overall injection process as well as of the effects of both injection strategy and spray orientation modifications on both the air/fuel and fuel/wall interaction.

A computational fluid dynamics code is applied to simulate fluid flow and combustion in a four-stroke single cylinder engine with flat combustion chamber geometry. Heat flux and heat transfer coefficient on the cylinder head, cylinder wall, piston, intake and exhaust valves are determined. Result for a certain condition is compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurement in the literature and close agreement is observed. It is observed that the value of heat flux and heat transfer coefficient varies considerably in different positions of the combustion chamber, but the trend with crank angle is almost the same.

It is well known that presence of backlash in the timing gear train of modern internal combustion engines leads to significant increase in dynamic loads and noise. Accounting for the backlash introduces non-linearity in the numerical model. Traditionally such a system is solved as an initial value problem using multi-cycle numerical integration of the equation of motion in time domain. Present work offers an efficient method for analysis of periodic oscillations of multi-mass system of complex structure by converting it into a chainlike system. At first, the method is applied to a linear system. It is also shown that this method is applicable to a nonlinear system offering significant improvement in the simulation time as compared to the traditional approach. The developed method is applied to studying dynamics of timing gear train of a high power density diesel engine.

The use of natural gas in medium and heavy duty engines for public transportation is a promising way for reducing exhaust emissions. Computer simulations, coupled with engine tests, have arisen as a valuable methodology to study the gas exchange processes inside intake and exhaust manifolds. A wave action model is set up in order to simulate a natural gas fuelled turbocharged engine. Once the modeling results show good agreement when comparing with measured data at different running conditions in terms of fluid dynamic properties, the model is used to study the air-fuel mixture process in the intake manifold and optimize the injection system behavior. Comparisons of modeled air-fuel composition in the cylinders are performed with both single and multi-point injection strategies. These cylinder to cylinder air-fuel mixture dispersion problems are analyzed at both steady and transient engine running conditions. Steady operation is performed correctly when using single-point injection since the gas mixer upstream the throttle valve enhances the mixing process. However, significant gas dispersion among cylinders appears during an engine load transient. With multi-point injection the critical parameter is the injection timing, since it is usually larger than the intake stroke period and, if it is not conveniently arranged, significant natural gas dispersion among cylinders may appear at both steady and transient running conditions.

Facing monumental challenges in the tightening constraints of friction reduction, oil control, and blowby, piston ring designs are becoming intricately more complex. Within this complex matrix of design criteria, minute changes can have a big impact on the performance of engines, which are operating under conditions of higher temperatures and speeds. At the same time there is a general requirement to reduce the overall mass of the components. Thus, the piston rings must have inherent design properties (more finely tuned) to withstand the elevated operations of the engine, maintain longevity, and perform within the expected performance criteria. To help meet these challenges, this paper gives a brief introduction to the axial formed process as an improvement of the twist characteristic on the upper compression ring (UCR) design, along with representative supporting performance data based on engine tests and computer simulation. The goal is to show some successes across different engine types involving the axial formed process. The main topics covered include a) historical role and design of twisted rings in the engine, b) advantages of improved twisted rings, c) example of engine test data and d) example simulation results.

The injection process optimization plays a key role in diesel engine development activities, both for pollutant formation control and performance improvement. The present paper focuses on relatively small diesel units, equipped with fully mechanical injection systems; in detail, the considered system layout is based on the use of spring injectors; the amount of delivered fuel is controlled by the positioning of the pump plunger groove. The paper highlights the role of the inline pump and the influence of fuel characteristics on the system operation. By means of a three-dimensional numerical flow study, the behavior of pump fuel passages and delivery valve is simulated. Then, on the basis of the system features, a complete lumped/one-dimensional numerical model is realized, in which the discharge coefficients evaluated through the three-dimensional simulation are employed. Fuel injection rate and local pressure time histories are investigated, paying specific attention to the occurrence of the relevant phenomena in the system components. Obtained results are compared with experimental data.

The paper has explored the solutions to the thermal overload in the cylinder head of a heavy-duty vehicle 6-cylinder diesel engine and the thermal cracks in the valve-bridge of the engine. The experiments include measuring the temperature of the cylinder head bottom and testing the flow distribution of coolant through the upper nozzles of cylinder head bottom. The follow-up analysis was conducted on the causes of the excessive thermal load of the cylinder head bottom, the thermal cracks in the valve-bridge region, and the rationality of the structure of the water jacket for the cylinder head. The mechanism of the water jacket of cylinder head was further inquired. Then 3-D CFD numerical simulation of water jacket in the sixth cylinder, which is in the worst cooling condition, is performed. To enhance the flow form in water jacket and lower the cost of enhancement, we proposed 4 schemes of water jacket and conducted the numerical simulations to these schemes. It was identified that all these schemes have efficiently improved the flow field in water jacket. In the typical proposed scheme 1 in which 6 nozzles of all the 10 upper nozzles were blocked, the coolant flow rate on the bottom of the water jacket and in the cylinder head valve-bridge region increased by about 68.73%. The measuring results of the cylinder head bottom temperature show that the maximum temperature in the valve-bridge region of cylinder head is reduced by 9.2 °C and the temperature gradient reduction is 19.55 percent, suggesting that the thermal load and thermal stress of the studied diesel engine cylinder head has been significantly lowered.