Francesco Concetto Pesce

Experimental and Numerical Assessment of Multi-Event Injection Strategies in a Solenoid Common-Rail Injector

Nowadays, injection rate shaping and multi-pilot events can help to improve fuel efficiency, combustion noise and pollutant emissions in diesel engine, providing high flexibility in the shape of the injection that allows combustion process control. Different strategies can be used in order to obtain the required flexibility in the rate, such as very close pilot injections with almost zero Dwell Time or boot shaped injections with optional pilot injections. Modern Common-Rail Fuel Injection Systems (FIS) should be able to provide these innovative patterns to control the combustion phases intensity for optimal tradeoff between fuel consumption and emission levels.In this work, a 1D-CFD model in GT-SUITE of a solenoid ballistic Common-Rail injector was firstly refined respect to the previous work [1] and then it was validated against an extensive experimental dataset of single injections, standard double pilot and multi-pilot injection patterns (up to 4 pilot events) with almost zero dwell time between two consecutive injection events. The experimental hydraulic test data used to validate the one-dimensional model were obtained by means of the UniPG Injection Analyzer based on the Zeuchs method.The comparison between the experimental and simulated volumetric injection rates showed a more than satisfactory accuracy of the model in predicting the actual behavior of the ballistic injector for all the injection patterns tested, even for relatively complex injector command strategies, characterized by reduced Dwell Time values between consecutive injection events.

Numerical Investigation on the Effects of Different Thermal Insulation Strategies for a Passenger Car Diesel Engine

AbstractOne of the key technologies for the improvement of the diesel engine thermal efficiency is the reduction of the engine heat transfer through the thermal insulation of the combustion chamber. This paper presents a numerical investigation on the effects of the combustion chamber insulation on the heat transfer, thermal efficiency and exhaust temperatures of a 1.6 l passenger car, turbo-charged diesel engine. First, the complete insulation of the engine components, like pistons, liner, firedeck and valves, has been simulated. This analysis has showed that the piston is the component with the greatest potential for the in-cylinder heat transfer reduction and for Brake Specific Fuel Consumption (BSFC) reduction, followed by firedeck, liner and valves. Afterwards, the study has been focused on the impact of different piston Thermal Barrier Coatings (TBCs) on heat transfer, performance and wall temperatures. This analysis has been performed using a 1-D engine simulation code coupled with a lumped mass thermal model, representing the engine structure. A time-periodic wall conduction model has been used to calculate the wall temperature swings along the combustion chamber surface and within the engine cycle. Two different TBC materials, Yttria-Partially Stabilized Zirconia (Y-PSZ) and anodized aluminum, and different layer thicknesses have been simulated.

Digital Shaping and Optimization of Fuel Injection Pattern for a Common Rail Automotive Diesel Engine through Numerical Simulation

Development trends in modern Common Rail Fuel Injection System (FIS) show dramatically increasing capabilities in terms of optimization of the fuel injection pattern through a constantly increasing number of injection events per engine cycle along with a modulation and shaping of the injection rate. In order to fully exploit the potential of the abovementioned fuel injection pattern optimization, numerical simulation can play a fundamental role by allowing the creation of a kind of a virtual injection rate generator for the assessment of the corresponding engine outputs in terms of combustion characteristics such as burn rate, emission formation and combustion noise (CN). This paper is focused on the analysis of the effects of digitalization of pilot events in the injection pattern on Brake Specific Fuel Consumption (BSFC), CN and emissions for a EURO 6 passenger car 4-cylinder diesel engine. The numerical evaluation was performed considering steady-state conditions for 3 key points representative of typical operating conditions in the low-medium load range. The optimization process was carried out through numerical simulation, by means of a suitable target function aiming to minimize BSFC and CN while not exceeding the target NOx emissions level. By means of a previously developed fuel injection system model, possible different injection patterns with high number of pilot injections were evaluated thus obtaining a kind of virtual injection rate generator, the outcomes of which were then used as input for a DIPulse combustion model in order to predict BSFC, combustion noise and emissions. Through numerical optimization of pilot injection pattern digitalization, potential for achieving significant reductions in BSFC and CN for low load engine points while not exceeding the target NOx emissions level, was demonstrated.

On the Reduction of Combustion Noise by a Close-Coupled Pilot Injection in a Small-Bore DI Diesel Engine

For a pilot-main injection strategy in a single cylinder light duty diesel engine, the dwell between the pilot- and main-injection events can significantly impact combustion noise. As the solenoid energizing dwell decreases below 200 μs, combustion noise decreases by approximately 3 dB and then increases again at shorter dwells. A zero-dimensional thermodynamic model has been developed to capture the combustion-noise reduction mechanism; heat-release profiles are the primary simulation input and approximating them as top-hat shapes preserves the noise-reduction effect. A decomposition of the terms of the underlying thermodynamic equation reveals that the direct influence of heat-release on the temporal variation of cylinder-pressure is primarily responsible for the trend in combustion noise. Fourier analyses reveal the mechanism responsible for the reduction in combustion noise as a destructive interference in the frequency range between approximately 1 kHz and 3 kHz. This interference is dependent on the timing of increases in cylinder-pressure during pilot heat-release relative to those during main heat-release. The mechanism by which combustion noise is attenuated is fundamentally different from the traditional noise reduction that occurs with the use of long-dwell pilot injections, for which noise is reduced primarily by shortening the ignition delay of the main injection. Band-pass filtering of measured cylinder-pressure traces provides evidence of this noise-reduction mechanism in the real engine.When this close-coupled pilot noise-reduction mechanism is active, metrics derived from cylinder-pressure such as the location of 50% heat-release, peak heat-release rates, and peak rates of pressure rise cannot be used reliably to predict trends in combustion noise. The quantity and peak value of the pilot heat-release affect the combustion noise reduction mechanism, and maximum noise reduction is achieved when the height and steepness of the pilot heat-release profile are similar to the initial rise of the main heat-release event. A variation of the initial rise-rate of the main heat-release event reveals trends in combustion noise that are the opposite of what would happen in the absence of a close-coupled pilot. The noise-reduction mechanism shown in this work may be a powerful tool to improve the tradeoffs among fuel efficiency, pollutant emissions, and combustion noise.Copyright