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Flexibility in running with different fuel is becoming an important issue in the Internal Combustion Engine design due to the increasingly wider use of alternative fuels. The injection systems must deal with fuels having different properties and effects on engine behavior and take proper adjustments in the control strategy. Particularly the transient during which one fuel is being replaced by the second one is a critical point of the injection system operation, and its capability of recognizing the fuel mixture currently available is a fundamental matter in the engine control development. This paper focuses on the multidimensional CFD analysis of a Common Rail type multi-fuel injection system accumulator during the gasoline - ethanol shift. An open source computational fluid dynamics code was used in the modeling.

A 0.5 liter optical HCCI engine firing a mixture of n-heptane (50%) and iso-octane (50%) with air/fuel ratio of 3 is studied using large eddy simulation (LES) and laser diagnostics. Formaldehyde and OH LIF and in-cylinder pressure were measured in the experiments to characterize the ignition process. The LES made use of a detailed chemical kinetic mechanism that consists of 233 species and 2019 reactions. The auto-ignition simulation is coupled with LES by the use of a renormalized reaction progress variable. Systematic LES study on the effect of initial temperature inhomogeneity and turbulence intensity has been carried out to delineate their effect on the ignition process. It was shown that the charge under the present experimental condition would not be ignited without initial temperature inhomogeneity. Increasing temperature inhomogeneity leads to earlier ignition whereas increasing turbulence intensity would retard the ignition.

Hydrogen has been proposed as a possible fuel for automotive applications. This paper reports an experimental investigation of hydrogen as HCCI engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on an extremely fast burning fuel such as hydrogen as well as to study the efficiency, the combustion phasing and the formation of emissions. The experiments were conducted on a single-cylinder research engine with a displacement volume of 1.6 litres and pancake combustion chamber geometry. Variation of lambda, engine speed, compression ratio and intake temperature were parts of the experimental setting. The engine was operated in Homogenous Charge Compression Ignition (HCCI) mode and as comparison also in Spark Ignition (SI) mode. Hydrogen was found to be a possible fuel for an HCCI engine. The heat release rate was extremely high and the interval of possible start of combustion crank angles was found to be narrow.

In this paper, the dependency on fuel blends of a four stroke, four cylinder SI engine equipped with a low pressure common rail type injection system is analyzed. With reference to an operating condition using E21 (21% ethanol, 79% gasoline) as a fuel, the experimental performance of the engine are firstly introduced, and the brake power, the specific fuel consumption, the total efficiency, the heating combustion power and the injected mass per stroke dependency on shaft speed are introduced. Then, the multi-fuel injection system actual behavior is predicted by means of a properly tailored lumped and distributed numerical model, whose general reliability is defined mainly in terms of injected mass per stroke. Afterward, the engine performance variation with the fuel mixture is determined, and the adaptation of the PWM control applied to injectors is proposed to compensate the engine operating characteristics.

The purpose of this paper is to compare different methodologies of CFD analysis, applied to the intake plenum of a turbocharged HSDI Diesel engine. The study is performed by using both an engine cycle simulation code and a 3D-CFD code. Experiments at the engine dynamometer and at a steady flow bench support the theoretical study. The most promising simulation technique presented in the paper is the integrated 1D and 3D-CFD simulation. This numerical approach showed itself to be particularly suitable for analysing complex engine components where the flow patterns are fully transient.

For the simultaneous evaluation of the influence on engine knock of both chemical conditions and global operating parameters, a combined tool was developed. Thus, a two-zone kinetic model for SI engine combustion calculation (Ignition) was implemented into an engine cycle simulation commercial code. The combined model predictions are compared with experimental data from a single-cylinder test engine. This shows that the model can accurately predict the knock onset and in-cylinder pressure and temperature for different lambda conditions, with and without EGR. The influence of nitric oxide amount from residual gas in relation with knock is further investigated. The created numerical tool represents a useful support for experimental measurements, reducing the number of tests required to assess the proper engine control strategies.

The paper deals with the simulation and the experimental verification of the dynamic behaviour of a linear actuator equipped with different configurations of mechanical cushion. A numerical model, developed and tailored to describe the influence of different modulation of the discharged flow-rate (and of the correspondent discharging orifice design) on the cushioning characteristics variation is firstly introduced. Then, with respect to the case of the cylindrical cushioning engagement, both the reliability and the limits of the numerical approach are highlighted through a numerical vs. experimental comparison, involving the piston velocity and the cylinder chambers pressure. After, with the aim of highlighting the effect of mechanical cushions design on a two effect linear actuator dynamic performances, the characteristics modulation of four alternative cushioning systems are determined and deeply analyzed.

This paper reports an analysis of the lubrication mechanism and the dynamic behaviour of axial piston pumps and motors slipper bearings. A numerical procedure is used to solve the Reynolds equation, written here with respect to the slipper-swash plate gap, whose height is considered variable in a two dimensional field and with time. The contributions of forces and moments acting on the slipper are illustrated and discussed, then the numerical method is presented to solve the Reynolds equation. Taking into consideration the slipper surface that is facing the swash plate, different geometry profiles are considered and the subsequent dynamic behaviour of the slipper is investigated; in particular, it is shown that a flat profile cannot always guarantee the bearing capability of the slipper and the lubrication in the gap is compromised for some critical operating conditions.

The paper focuses on the mixing process of different fuels in a multi-fuel low pressure common rail injection system for a four stroke SI engine. The study is devoted to the prediction of the fuel mixture delivered by the injectors during a transient in which gasoline is being replaced by ethanol or a gasoline/ethanol blend. An integrated approach of different numerical tools is used to model the rail dynamic behavior under actual operating conditions. First, the 1D model of the injection system is constructed and the time varying conditions at the accumulator inlet and at the injectors' boundaries are assessed. The second step of the study is centered on the CFD analysis of the mixing process within the rail. The effects of the different engine operations on the fuels mixing are investigated and the injected fuel distribution among the cylinders is calculated. An open source computational fluid dynamics code is used in the simulations.

High power output, four stroke, motorcycle engines are characterised by specific power levels well beyond 150 HP/litre also in production engines. These power levels are obtained through extremely high values of volumetric efficiencies in the range of high engine speed, resulting from highly optimised gas exchange processes. In the present paper, a four cylinder, four valve per cylinder engine with a four-in-one exhaust is optimised for volumetric efficiencies by using state-of-the-art computational methods. These computational methods include static three dimensional computations as well as dynamic one and three dimensional computations. The engine geometric and operating parameters optimised by using these computations agree fairly well with those optimised by using experiments, thus demonstrating the effectiveness of the proposed computational practice.

In this work, constant volume combustion is studied using a zero-dimensional FORTRAN code, which is a wide-ranging chemical kinetic simulation that allows a closed system of gases to be described on the basis of a set of initial conditions. The model provides an engine- or reactor-like environment in which the engine simulations allow for a variable system volume and heat transfer both to and from the system. The combustion chamber is divided into two zones as burned and unburned ones, which are separated by an assumed thin flame front in the combustion model used for this work. Equilibrium assumptions have been adopted for the modeling of the thermal ionization, where Saha's equation was derived for singly ionized molecules. The investigation is focused on the thermal ionization of NO as well as for other species. The outputs generated by the model are temperature profiles, species concentration profiles, ionization degree and an electron density for each zone.

Hydrogen has been proposed as a possible fuel for automotive applications. Methanol is one of the most efficient ways to store and handle hydrogen. By catalytic reformation it is possible to convert methanol into hydrogen and carbon monoxide. This paper reports an experimental investigation of Reformed Methanol Gas as Homogeneous Charge Compression Ignition (HCCI) engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on a mixture of hydrogen and carbon monoxide, to study the combustion phasing, the efficiency and the formation of emissions. Reformed Methanol Gas (RMG) was found to be a possible fuel for an HCCI engine. The heat release rate was lower than with pure hydrogen but still high compared to other fuels. The interval of possible start of combustion crank angles was found to be narrow but wider than for hydrogen. The high rate of heat release limited the operating range to lean (λ>3) cases as with hydrogen.

This paper studies the proportional directional control valves design influence on the energetic behavior of a mid-power compact excavator. In particular, with reference to the hydraulic circuit actuating the primary workgroup, in the paper the hydraulic power metering performed with the boom cylinder proportional control valve is studied, and some design solution useful in reducing both the hydraulic power dissipation, and the power absorption from the machinery prime mover are highlighted. The analysis, experimentally performed for different operating conditions, is carried out highlighting the influence of a metering configuration both on the supply pressure modulation and on the flow-rate supplied to the actuator.

In this paper, an orifice-based lumped parameter model has been developed and tailored to predict the feeding performances of a single stage, inwardly opening, PWM controlled gas injector for automotive applications. In particular, simplifying the description of injector relevant sections, and adopting a “semi-perfect” approach to depict the gas properties dependency on pressure and temperature, the sub-sonic efflux through the injector metering section is studied involving both an isentropic and a polytropic expansion. Then, considering dry air as fluid medium, the injector feeding characteristics variations with the duty cycle, with the feeding pressure and with temperature are highlighted.

A major trend in current automotive research is hybridization of the power supply. This combination of electrical machine and combustion engine results, in some hybridization topologies, in a total decoupling of the combustion engine from the transmission. When the engine is decoupled from the transmission a new degree of freedom arises in engine design. The piston movement does not have to follow an evenly rotating shaft any more. It can be altered by the generator to achieve a movement found to be better from the point of efficiency or environmental concerns. Modelling work showed a potential of lowered NO emissions if the expansion could be delayed. The experimental study, conducted in a two piston Alvar engine, showed that the state of the art electrical machine (EM) propelling one of the crankshafts was too weak to change the crankshaft speed in an extent to give the fast volume changes required to change the emissions of the internal combustion engine (ICE).

The internal flow field of a low pressure common rail type multi-fuel injector is analyzed by means of numerical simulation and particular attention is devoted to the cavitation and aeration phenomena when using different fuel mixtures. The fluid-dynamics open source OpenFOAM code is used; and the original cavitation model (based on a barotropic equation of state and homogeneous equilibrium assumption) is extended in order to account also for gases dissolved in the liquid medium. The effect of air dissolution into liquid is determined by introducing the Henry law for the equilibrium condition and the time dependence of solubility is calculated on a Bunsen Coefficient basis. A preliminary study of test cases available in literature is carried out to address the model predictive capabilities and grid dependency. The calculated pressure distribution and discharge coefficient for different nozzle shapes and operating conditions are compared with the referenced experimental measurements.

Standard design practice usually adopts steady flow tests for addressing optimisation of the intake valve-port assembly. Recently, with more user-friendly CFD tools and with increased computing power, intake stroke simulations, handling both piston and valves motion, have become practical. The purpose of this paper is to compare the design guidelines provided by the standard steady flow tests (both experimental and numerical) and the information coming from a CFD-3D intake stroke analysis. Reference is made to a four valve HSDI Diesel engine. Three swirl control strategies are investigated. It is supposed that one intake valve is kept closed, while the other one operates normally (first strategy). The second strategy consists in a 50% reduction of the lift of both valves. Finally, the third possibility is the blockage of one intake port by means of a simple butterfly valve.