Michele Battistoni

Injection Strategies Tuning for the Use of Bio-Derived Fuels in a Common Rail HSDI Diesel Engine

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.

Analysis of Diesel Spray Momentum Flux Spatial Distribution

In the present paper the results of an experimental and numerical analysis of a common -rail, high pressure Diesel spray evolving in high counter pressure conditions is reported. The experimental study was carried out mainly in terms of spray momentum flux indirect measurement by the spray impact method; the measurement of the impact force time-histories, along with the CFD analysis of the same phenomenon, gave interesting insight in the internal spray structure. As well known, the overall spray structure momentum flux along with the injection rate measurements can be used to derive significant details about the in-nozzle flow and cavitation phenomena intensity. The same global spray momentum and momentum flux measurement can be useful in determining the jet -tojet ununiformities also in transient, engine-typical injection conditions which can assist in the matching process between the injection system and the combustion chamber design. In the present paper, the potential in the internal spray structure analysis by means of local spray momentum flux distribution investigation is evaluated. To obtain such momentum flux distribution maps, a variant in the global spray momentum measurement technique is evaluated. The use of an adaptor to the momentum flux measurement rig is discussed, numerically analyzed and tested on a dedicated experimental bench. Some results pertaining to solenoid-actuated common rail injectors are presented and discussed in terms of spray distribution irregularities, momentum profiles and differences in the spray structure obtained for the different jets emerging from the nozzle.

Modeling of internal and near-nozzle flow for a GDI fuel injector

A numerical study of two-phase flow inside the nozzle holes and the issuing spray jets for a multi-hole direct injection gasoline injector has been presented in this work. The injector geometry is representative of the Spray G nozzle, an eight-hole counterbore injector, from the Engine Combustion Network (ECN). Simulations have been carried out for a fixed needle lift. Effects of turbulence, compressibility and non-condensable gases have been considered in this work. Standard k–e turbulence model has been used to model the turbulence. Homogeneous Relaxation Model (HRM) coupled with Volume of Fluid (VOF) approach has been utilized to capture the phase change phenomena inside and outside the injector nozzle. Three different boundary conditions for the outlet domain have been imposed to examine non-flashing and evaporative, non-flashing and non-evaporative and flashing conditions. Noticeable hole-to-hole variations have been observed in terms of mass flow rates for all the holes under all the operating conditions considered in this study. Inside the nozzle holes mild cavitation-like and in the near-nozzle region flash boiling phenomena have been predicted when liquid fuel is subjected to superheated ambiance. Under favorable conditions considerable flashing has been observed in the near-nozzle regions. An enormous volume is occupied by the gasoline vapor, formed by the flash boiling of superheated liquid fuel. Large outlet domain connecting the exits of the holes and the pressure outlet boundary appeared to be necessary leading to substantial computational cost. Volume-averaging instead of mass-averaging is observed to be more effective, especially for finer mesh resolutions.Copyright

Numerical simulation of internal and near-nozzle flow of a gasoline direct injection fuel injector

A numerical study of two-phase flow inside the nozzle holes and the issuing spray jets for a multi-hole direct injection gasoline injector has been presented in this work. The injector geometry is representative of the Spray G nozzle, an eight-hole counterbore injector, from, the Engine Combustion Network (ECN). Simulations have been carried out for the fixed needle lift. Effects of turbulence, compressibility and, non-condensable gases have been considered in this work. Standard k—ɛ turbulence model has been used to model the turbulence. Homogeneous Relaxation Model (HRM) coupled with Volume of Fluid (VOF) approach has been utilized to capture the phase change phenomena inside and outside the injector nozzle. Three different boundary conditions for the outlet domain have been imposed to examine non-flashing and evaporative, non-flashing and non-evaporative, and flashing conditions. Inside the nozzle holes mild cavitation-like and in the near-nozzle region flash boiling phenomena have been predicted in this study when liquid fuel is subjected to superheated ambiance. Noticeable hole to hole variation has been also observed in terms of mass flow rates for all the holes under both flashing and non-flashing conditions.

Dependence of Flow Characteristics of a High Performance S.I. Engine Intake System on Test Pressure and Tumble Generation Conditions - Part 1: Experimental Analysis

In this paper an experimental analysis is carried out to evaluate the dependence of the flow characteristics in the intake system of a high performance 4 valve, Spark Ignition Internal Combustion Engine, on the experimental conditions at the steady flow test bench. Experimental tests are performed at different pressure levels on a Ducati Corse racing engine head, to measure the Discharge Coefficient C d and the Tumble Coefficient N T , expanding the work already presented in a previous work by the same research group: with a new test bench, the maximum test pressure level is increased up to 24 kPa, while differently-shaped tumble adaptors are used to evaluate N t . The study is aimed at determining the influence of the test pressure on C d and N T measurements, and in particular of the tumble adaptor shape. As a matter of fact, researchers usually adopt different shapes, such as the conventional T type or the L one, resulting in a non uniform base to compare results from several investigations. This work is aimed at verifying the quantitative differences that can be found by using these shapes, in particular when the separate contribution to the tumble vortex generation from one only of two intake valves has to be evaluated. The above described analysis is also useful to evaluate the C d values obtained in the different test conditions used.

Numerical Study of SI Engine Part Load Operating Conditions Using Different VVA Strategies

In SI engines, VVA (Variable Valve Actuation) technology is mainly used for the reduction of pumping losses at part load. This paper presents the results of fluid dynamic analyses on a 4V engine about the effects of different VVA strategies, by comparing and discussing the results in terms of organized charge motions, turbulence levels, flame developments, NO and CO emissions. CFD simulations cover five load control cases: comparison is among conventional throttling, EIVC (Early Intake Valve Closure) with symmetric and asymmetric intake lifts, LIVC (Late Intake Valve Closure) and symmetrical Multi-Lift strategies. 3D U-RANS simulations are performed, adopting the Extended Coherent Flamelet Model (ECFM) for the description of premixed SI combustion. The 3D model is also coupled to a 1D engine model which provides inlet/outlet boundary conditions. Simulation results highlight the potential of asymmetric Early Intake Valve Closure (EIVC) strategy which allows reducing pumping losses and, at the same time, achieving good turbulence intensity and combustion speed, if compared to other load control strategies. Multi-Lift strategy resulted excellent in terms of burn duration, but pumping losses are practically the same as in the throttled engine.Copyright

Modeling of Flash Boiling Phenomenon in Internal and Near-Nozzle Flow of Fuel Injectors

Detailed analysis of the internal and the near-nozzle flow of fuel injectors is a necessity for a comprehensive understanding of any internal combustion engine performance. For gasoline direct injection engines, under part-load conditions, the in-cylinder pressure can be subatmospheric when the high-temperature fuel is injected, resulting in flash boiling. Detailed experimental characterization of such complex phenomena is extremely difficult. Three-dimensional computational fluid dynamics (CFD) simulations provide key insights into the flash boiling phenomena. The Spray G injector from Engine Combustion Network (ECN) has been considered for this study, which has eight counter-bored holes. Homogeneous relaxation model is used to capture the rate of phase change. Standard and RNG \(k-\epsilon \) turbulence models have been employed for modeling turbulence effects. Based on apriori thermodynamic estimates, three types of thermodynamic conditions have been explored: non-flashing, moderate flashing, and intense flashing. Numerical analyses showed that with more flashing the spray plumes grow wider due to the volume expansion of the rapidly forming fuel vapor. Mainly single-component fuel is studied in this work. Iso-octane is considered as the gasoline surrogate for this study. Binary component blends of isooctane and ethanol were also tested for blended fuel flashing predictions using the existing numerical setup. After careful estimation of blended fuel saturation properties, the simulations indicated that blended fuels can be more volatile than the individual components and thus exhibit more flashing compared to the cases with single-component fuels.