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Several studies have been performed to investigate the effects of using hydrogen in spark ignition (SI) engines. One general conclusion that emerged was that stoichiometric operation of premixed charge hydrogen engines features increased losses compared to other fuels such as methane. Most studies attribute this higher loss to increased rates of heat transfer from the working fluid to the combustion chamber walls. Indeed, heat flux measurements during combustion and expansion recorded much higher values for hydrogen compared to methane stoichiometric operation. With regard to fluid properties, using the same net heat release equation as for gasoline engines results in an over prediction of heat losses to the combustion chamber walls. Also, the variation of specific heats ratio greatly influences calculated values for the rate of heat release. Therefore, a more detailed analysis of heat losses is required when comparing hydrogen to other fuels.

Detailed experimental information on the early stages of spark ignition process represent a substantial part for guiding the development of engines with higher efficiencies and reduced pollutant emissions. Flame kernel formation influences strongly combustion development inside the cylinder, especially for a direct injection spark ignition engine. This study presents the analysis of the evolution of spark-ignited flame kernels with detailed view upon cycle-to-cycle variations. Experiments are performed in a SI optical engine equipped with the cylinder head and injection system of a commercial turbocharged engine. Blend of commercial gasoline and butanol (40% by volume) is tested at stoichiometric and lean mixture conditions. Experiments are carried out at 2000 rpm through conventional tests (based on in-cylinder pressure measurements and exhaust emission analysis) and through optical diagnostics. In particular, UV-visible digital imaging and natural emission spectroscopy are applied.

This work aims at analyzing the fluid dynamic characteristics of a Ducati 4 valves SI engine, for racing motorcycle, during the intake and compression strokes, focusing on the correlation between steady state flow test data (experiments and simulations) and transient CFD simulation results, including the effect of variable valve actuation strategies with independent intake valve actuation. Several steady state flow test data were available in terms of maps of the discharge, tumble and swirl coefficients, at any combination of asymmetric lifts of the two intake valves. From these steady state data it can be argued that asymmetric strategies could enhance engine full load and part load operation characteristics, by exploiting favourable trade off occurring between the opposing needs for high mass flow rate and high charge motion intensity.

In this study, experiments were carried out in an optical single-cylinder Direct Injection Spark Ignition engine fuelled with n-butanol and gasoline, alternatively. The engine is equipped with the head of a commercial turbocharged engine with similar geometrical specifications (bore, stroke, compression ratio). The head has four valves and a centrally located spark device with surface charge ignition. A conventional elongated hollow Bowditch piston is used and an optical crown, accommodating fused-silica window, is screwed onto it. The injector is side mounted and features 6 holes oriented to guide the jets towards the piston crown. During the experimental activity, the injection pressure was maintained at 100 bar for all conditions; the injection timing and the number of injections were adjusted to investigate their influence on combustion and emissions.

Within the context of distributed power generation, small size systems driven by spark ignition engines represent a valid and user-friendly choice, that ensures good fuel flexibility. One issue is that such applications are run at part load for extensive periods, thus lowering fuel economy. Employing an inverter (fitted between the generator and load) allows engine operation within a wide range of crankshaft rotational velocity, therefore improving efficiency. For the purpose of evaluating the benefits of this technology within a co-generation framework, two configurations were modeled by using the GT-Power simulation software. After model calibration based on measurements on a small size engine for two-wheel applications, the downsized version was compared to a larger power unit operated at constant engine speed for a scenario that featured up to 10 kW rated power.

This paper reports investigations on diesel jet transients, accounting for internal nozzle flow and needle motion. The calculations are performed with Large Eddy Simulation (LES) turbulence model by coupling the internal and external multiphase flows simultaneously. Short and multiple injection strategies are commonly used in internal combustion engines. Their features are significantly different from those generally found in steady state conditions, which have been extensively studied in the past, however, these conditions are seldom reached in modern engines. Recent researches have shown that residual gas can be ingested in the injector sac after the end-of-injection (EOI) and undesired dribbles can be produced. Moreover, a new injection event behaves differently at the start-of-injection (SOI) depending on the sac initial condition, and the initial spray development can be affected for the first few tens of μs.

Considering the generalized diversification of the energy mix, the use of alcohols as gasoline replacement is proposed as a viable option. Also, alternative control strategies for spark ignition engines (SI) such as lean operation and exhaust gas recirculation (EGR) are used on an ever wider scale for improving fuel economy and reducing the environmental impact of automotive engines. In order to increase the stability of these operating points, alternative ignition systems are currently investigated. Within this context, the present work deals about the use of plasma assisted ignition (PAI) in a direct injection (DI) SI engine under lean conditions and cooled EGR, with gasoline and n-butanol fueling. The PAI system was tested in an optically accessible single-cylinder DISI engine equipped with the head of a commercial turbocharged power unit with similar geometrical specifications (bore, stroke, compression ratio).

The recent introduction of electronic controlled, high pressure injection systems has deeply changed the scenario for light duty, automotive diesel engines. This change is mainly due to the enhanced flexibility in obtaining the desired injection law (time history and injected fuel quantity), while high injection pressures also favour a suitable mixture formation. This results in higher engine performance (efficiency and power) and in better pollutant emissions control. At the same time, in order to reduce the greenhouse gases net production, research is analyzing alternative resources, such as bio-derived fuels. In particular, methyl esters derived by different vegetable oils are characterized by high cetane numbers and very small sulfur content. The present work reports the results of a comparative analysis performed on a modern DI, common-rail, turbocharged engine by using three different bio-derived fuels (rape seed, soybean, waste cooked oil) and conventional fossil diesel fuel.

This work investigates the effects of cavitation on spray characteristics by comparing measurements of liquid and vapor penetration as well as ignition delay and lift-off length. A smoothed-inlet, converging nozzle (nominal KS1.5) was compared to a sharp-edged nozzle (nominal K0) in a constant-volume combustion vessel under thermodynamic conditions consistent with modern compression ignition engines. Within the near-nozzle region, the K0 nozzle displayed larger radial dispersion of the liquid as compared to the KS1.5 nozzle, and shorter axial liquid penetration. Moving downstream, the KS1.5 jet growth rate increased, eventually reaching a growth rate similar to the K0 nozzle while maintaining a smaller radial width. The increasing spreading angle in the far field creates a virtual origin, or mixing offset, several millimeters downstream for the KS1.5 nozzle.

Liquids with stable suspensions of nanoscale materials are defined as nanofluids. As reported in recent scientific literature, a very small amount of suspended nanostructures has the potential to enhance the thermo physical, transport and radiative properties of the base fluid. One of the main applications of this technology is in the field of combustion and fuels. In fact, adding nanomaterials (such as metals, oxides, carbides, nitrides, or carbon-based nanostructures) to liquid fuels is able to enhance ignition and combustion. The focus of this research is to gain a fundamental understanding of the characteristics of a nanofluid fuel prepared using carbon nanoparticles (CNPs) and multi-walled carbon nanotubes (MWCNTs) dispersed in butanol. This study starts with the investigation of the optical properties of the mixtures. The transmission spectra of the nanofluids are measured in a wide wavelength range from UV (250 nm) to near IR (800 nm).

Conventional fossil fuels are more and more regulated in terms of both engine-out emissions and fuel consumption. Moreover, oil price and political instabilities in oil-producer countries are pushing towards the use of alternative fuels compatible with the existing units. N-Butanol is an attractive candidate as conventional gasoline replacement, given its ease of production from bio-mass and key physico-chemical properties similar to their gasoline counterpart. A comparison in terms of combustion behavior of gasoline and n-Butanol is here presented by means of experiments and 3D-CFD simulations. The fuels are tested on a single-cylinder direct-injection spark-ignition (DISI) unit with an optically accessible flat piston. The analysis is carried out at stoichiometric undiluted condition and lean-diluted mixture for both pure fuels.

The increasing limitations in engine emissions and fuel consumption have led researchers to the need to accurately predict combustion and related events in gasoline engines. In particular, knock is one of the most limiting factors for modern SI units, severely hindering thermal efficiency improvements. Modern CFD simulations are becoming an affordable instrument to support experimental practice from the early design to the detailed calibration stage. To this aim, combustion and knock models in RANS formalism provide good time-to-solution trade-off allowing to simulate mean flame front propagation and flame brush geometry, as well as “ensemble average” knock tendency in end-gases. Still, the level of confidence in the use of CFD tools strongly relies on the possibility to validate models and methodologies against experimental measurements.

The new real driving emission cycles and the growing adoption of turbocharged GDI engines are directing the automotive technology towards the use of innovative solutions aimed at reducing environmental impact and increasing engine efficiency. Water injection is a solution that has received particular attention in recent years, because it allows to achieve fuel savings while meeting the most stringent emissions regulations. Water is able to reduce the temperature of the gases inside the cylinder, coupled with the beneficial effect of preventing knock occurrences. Moreover, water dilutes combustion, and varies the specific heat ratio of the working fluid; this allows the use of higher compression ratios, with more advanced and optimal spark timing, as well as eliminating the need of fuel enrichment at high load. Computational fluid dynamics simulations are a powerful tool to provide more in-depth details on the thermo-fluid dynamics involved in engine operations with water injection.

This work involves modeling internal and near-nozzle flows of a gasoline direct injection (GDI) nozzle. The Engine Combustion Network (ECN) Spray G condition has been considered for these simulations using the nominal geometry of the Spray G injector. First, best practices for numerical simulation of the two-phase flow evolution inside and the near-nozzle regions of the Spray G injector are presented for the peak needle lift. The mass flow rate prediction for peak needle lift was in reasonable agreement with experimental data available in the ECN database. Liquid plume targeting angle and liquid penetration estimates showed promising agreement with experimental observations. The capability to assess the influence of different thermodynamic conditions on the two-phase flow nature was established by predicting non-flashing and flashing phenomena.

The present work concerns the analysis of a concept for a new variable valve actuation system for internal combustion engines, denoted HVC (Hydraulic Valve Control system). The system is an electro-hydraulic device which aims at minimizing the power consumption required for the valve actuation. Unlike lost motion devices, where the excess pumped oil is wasted in order to control the lift profile, the HVC system uses a reduced quantity of energy to ensure the actual lift profile. For that reason interesting potentialities to increase the global fuel conversion efficiency of the engine are expected, in addition to the benefits deriving from the control flexibility. The HVC system has been modeled by means of an hydraulic simulation tool, useful for the dynamic analysis of mechanical and hydraulic systems. In this work the main elements of the device will be described and their relevant modeling parameters will be discussed.

Engines using compressed natural gas or liquefied petroleum gas are commonly equipped with control systems which are not yet able to completely monitor the gas supply line status. With a particular regard to safety but paying attention even to driving comfort and finally to polluting emissions reduction, two aspects in particular have been taken into account: the first one is the need to detect as soon as possible (and to react consequently) the presence of a problem occurring inside gas supply line (leakages and blocked-valves etcetera); the second one is the ability to detect an unsafe re-fuel operation, done with inserted ignition key, in order to switch off at least as more auxiliary loads as possible. The danger from such a manoeuvre may be identified in the high probability of an eventual electrostatic discharge and/or in the risk that the vehicle may be accidentally moved during the refilling operation.

Engine research community is developing innovative strategies capable of reducing fuel consumption and pollutant emissions while ensuring, at the same time, satisfactory performances. Spark ignition engines operation with highly diluted or lean mixture is demonstrated to be beneficial for engine efficiency and emissions while arduous for combustion initiation and stability. Traditional igniters are unsuitable for such working conditions, therefore, advanced ignition systems have been developed to improve combustion robustness. To overcome the inherent efficiency limit of combustion engines, the usage of renewable fuels is largely studied and employed to offer a carbon neutral transition to a cleaner future. For such a reason, both innovative ignition systems and bio or E-fuels are currently being investigated as alternatives to the previous approaches. Within this context, the present work proposes a synergetic approach which combines the benefits of a biofuel blend, i.e.

The potentialities in terms of engine performance and emissions reduction of pure biodiesel were examined on a Common Rail HSDI Diesel engine, trying to define a proper tuning of the injection strategies to bio-fuel characteristics. An experimental investigation was therefore carried out on a typical European passenger car Diesel engine, fuelled with a soybean oil derived biodiesel. A standard European diesel fuel was also used as a reference. In particular, the effects of an equal relative air/fuel ratio at full load condition were analysed; further, a sensitivity study on the outcome of the pilot injection timing and duration at part load on engine emissions was performed. Potentialities in recovering the performance gap between fossil fuel and biodiesel and in reducing NOx specific emissions, affecting only to a limited extent the biodiesel emission benefit in terms of CO, HC and FSN, were highlighted.

Water removal from Proton Exchange Membrane (PEM) Fuel Cell (FC) mainly involves two phenomena: some of the emerging droplets will roll on the Gas Diffusion Layer (GDL), others may impact channel walls and start sliding along the airflow direction. This different behaviour is linked to the hydrophobic/hydrophilic nature of the surface the water is moving on. In this paper, the walls of the channel of a FC were characterized by applying optical techniques. The deposition of droplets on the channel wall led to an evaluation of the proper range for Contact Angle Hysteresis (CAH = 55° - 45°), and due to the high wettability of the surface, droplets dimension was defined with a dimensionless parameter B/H. Under high crossflow condition (15 m/s) a sliding behaviour was observed. The channel features determined through image processing were used as boundary conditions for a 2D CFD two phase simulation employing the Volume of Fluid (VOF) model to keep track of the fluids interface.

Alternative combustion control in the form of lean operation offers significant advantages such as high efficiency and “clean” fuel oxidation. Maximum dilution rates are limited by increasing instability that can ultimately lead to partial burning or even misfires. A compromise needs to be reached between high tumble-turbulence levels that “speed-up” combustion and the inherent stochastic nature of this fluid motion. The present study is focused on gaining improved insight into combustion characteristics through thermodynamic analysis and flame imaging, in a wall-guided direct injection spark ignition engine with optical accessibility. Engine speed values were investigated in the range of 1000 to 2000 rpm, with commercial gasoline fueling, in wide open throttle conditions; mixture strength ranged from stoichiometric, down to the equivalence ratios that allowed acceptable cycle-by-cycle variations; and all cases featured spark timing close to the point of maximum brake torque.