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Technical Paper

The Influence of Stroke-to-Bore Ratio and Combustion Chamber Design on Formula One Engines Performance

This paper presents a numerical study of the combustion chamber design influence on the performance of racing engines. The analysis has been applied to the Ferrari 10 cylinder 3.0 liter S.I. engine adopted in Formula One racing. The numerical investigation aimed to asses the influence of stroke-to-bore ratio changes on engine performance within real life design constraints. The effects of the stroke-to-bore ratio on both the volumetric efficiency and the thermal conversion efficiency have been investigated. Flame front area maps, wall areas wetted by burned gases, mean flow field patterns and main turbulent parameters have been compared for two different S/B ratios. Since higher intake and exhaust valve areas per unit displaced volume result in a higher volume of piston bowls, a lower S/B ratio leads to a lower compression ratio, which strongly limits the indicated mean effective pressure.
Technical Paper

On The Flow Modeling Through The Valve Assembly In Engine Cycle Simulations

In this paper the 1-D modeling of flow through the assembly of valve and port in internal combustion engines is discussed. Three dimensional effects and flow losses close to the valve are accounted for through the experimental effective area, determined at a steady flow bench. The steady flow bench is standard equipment, widely used for engine design and development. The classic method is adequate to the purpose as long as the objective of measuring the effective area is a comparative process for the experimental improvement of the flow through the valves. On the contrary, if the effective area is used for engine cycle simulation, the experimental results must be considered with care. It is demonstrated in this study that, for the outflow from a cylinder to a valve, standard experimental practice can sometimes produce a significant error on the flow rate predicted by simulation.
Technical Paper

Numerical Study of the Combustion Chamber Shape for Common Rail H.S.D.I. Diesel Engines

The Common-rail injection system has allowed achieving a more flexible fuel injection control in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection. All these benefits have been gained by installing this device in combustion chambers born to work with the conventional distributor and in-line-pump injection systems. Their design was aimed to improve air-fuel mixing and therefore they were characterized by the adoption of high-swirl ports and re-entrant bowls. Experiments have shown that the high injection velocities induced by common rail systems determine an enhancement of the air fuel mixing. By contrast, they cause a strong wall impingement too. The present paper aims to exploit a new configuration of the combustion chamber more suited to CR injection systems and characterized by low-swirl ports and larger bowl diameter in order to reduce the wall impingement.
Technical Paper

Numerical Correlation of Combustion Evolution and Port and Combustion Chamber Shape in a High Speed, Four Valve, Spark Ignition Engine

High power output, four stroke, motorcycle engines are characterised by a complex combustion evolution strongly influenced by the properties of the averaged and turbulent flow field. In the present paper, state-of-the-art detailed computational methods are used to investigate the combustion evolution in a four cylinder, four valve per cylinder engine with a four-in-one exhaust where volumetric efficiencies and mixture compositions have been previously computed. Three dimensional unsteady computations of intake, compression, combustion and expansion strokes are performed. The method proves to be effective in qualitatively predicting heat release rate variations with engine speed and volumetric efficiency, while the simple modelling of the turbulent combustion does not allow to precisely define the magnitude of these variations.
Technical Paper

Multidimensional Cycle Analysis on a Novel 2-Stroke HSDI Diesel Engine

The Department of Mechanical and Civil Engineering (DIMeC) of the University of Modena and Reggio Emilia is developing a new type of small capacity HSDI 2-Stroke Diesel engine, featuring a specifically designed combustion system. The present paper is focused on the analysis of the scavenging process, carried out by means of 3D-CFD simulations, supported by 1D engine cycle calculations. First, a characterization of the flow through the ports and within the cylinder is performed under conventional operating conditions. Then, a complete 3D cycle simulation, including combustion, is carried out at four actual operating conditions, at full load. The CFD results provide fundamental information to address the development of the scavenging system, as well as to calibrate a comprehensive 1D engine model.
Technical Paper

Development of a 2-Stage Supercharging System for a HSDI Diesel Engine

2-stage supercharging applied to HSDI Diesel engines is a promising solution for enhancing rated power, low end torque, transient response and hence the launch characteristics of a vehicle. However, a trade-off is required to match some conflicting issues, i.e. overall dimensions, cost, emissions control and performance. The outcome strongly depends on the specific constraints and goals of the project. In the paper, reference is made to 2.8L, 4 cylinder in-line unit produced by VM Motori (Cento, Italy), equipped by a standard variable geometry turbocharger. A 1D thermo-fluid-dynamic model of the Euro V version of the engine was built and calibrated against experiments at the dynamometer bench, at both full and partial load.
Technical Paper

Comparison of Four Stroke MotoGP Engines

This paper compares different engine solutions for the FIM MotoGP World Championship. Starting from the general guidelines given in a previous paper [2], in this study the specific features of each engine architecture (3 and 4 in line, V4, V5 and V6) are considered. 1-D engine simulations, based on a previously validated model, are extensively used to optimize each solution, as well as to provide a comparison among the engines in terms of dynamometer performances. Some issues concerning engine balance, engine overall dimensions, intake and exhaust system lay-out are discussed. Finally, the influence of the engine on the bike acceleration is calculated by means of a simple simulation at the Mugello track. The comparison has shown slight differences among the proposed configurations. Globally, the V engines, with four and five cylinders, have resulted to be the best solutions.
Technical Paper

Comparison Between a Natural Gas and a Diesel Engine for Small Industrial Vehicles

The paper reviews the transformation of a 2.8 litre, 4 cylinder, turbocharged Diesel engine, produced by VM Motori (Cento, Italy), into a Compressed Natural Gas (CNG) naturally aspirated power unit. The main goal of the project is to keep an about constant top power value, minimizing engineering costs. The development of the new engine has been supported by experiments and 1D cycle simulations. A first prototype has been built and extensively tested at the dynamometer bench. These data helped the validation of the simulation model, which has been used as an optimisation tool, addressing the next steps of the development process.
Technical Paper

Comparison Between V12 and W12 F1 Engines

In this paper, a comparison has been carried out between two Formula 1 engine architectures: a traditional V12 and a 12 cylinder with three banks and one crankshaft, which will be referred to from here on as W12. This comparison is made in terms of geometrical features, as well as in terms of safety coefficients, torsional stiffness, state of balance and friction losses. The W12's crankshaft is 158 mm shorter and stiffer than the V12's. Furthermore, this crankshaft is simpler and lighter. The W12 engine front section is wider. The crankshaft of the W12 has a minimum safety factor that is 30% lower than the V12's under the same operating conditions (18000 rpm, bmep=13 bar). While the V12 is perfectly self-balanced, the secondary forces are out of balance in the W12's crankshaft. This unbalance is, however, no more critical than the one occurring in a V10 or V8. Friction losses in the W12 should be slightly lower in comparison to the V12.
Technical Paper

A New Concept of Supercharging Applied to High Speed DI Diesel Engines

The supercharging system investigated in this study is made up of a traditional turbocharger, coupled with a Roots-type positive displacement compressor. An electrically actuated clutch allows the compressor to be disengaged from the engine at high speed and under partial load steady operations (such as the ones occurring in a driving cycle). This concept of supercharging has been applied to the downsizing of a reference engine (a 2.5 litre, turbocharged, four cylinder, high speed DI Diesel engine), without penalization on the maximum brake power (110 kW) and transient response. For such a purpose, a “paper” engine has been theoretically characterized. The gross engine parameters have been optimised by means of 1-D numerical simulations, using a computational model previously validated against experiments. Performances of the reference and the downsized engine have been compared, considering both steady and transient operating conditions, full and partial load.