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Percussive breaking is basically a process in which short duration blows with high force intensity are applied in rapid succession, resulting in rock, concrete or pavement fragmentation. The machine for such a task is the hydraulic breaker which turns the hydraulic energy supplied by a positive displacement pump into mechanical energy as percussions of a piston against a chisel. This work presents the results of experimental tests carried out on a hydraulic breaker to determine its blow impact energy. Then, using these data, theoretical considerations are formulated in order to understand the phenomenon of the tool loading especially at the instant of the impact of the piston against the chisel, leading to the energy release.

In order to study the effects of air bulk motion and methane injection strategies on the development and pollutant levels of dual-fuel combustion, an intense experimental campaign was performed on a diesel common rail research engine with variable inlet configurations. Activating only the swirl or the tumble inlet valve of the engine, or both of them, it was possible to obtain, inside the cylinder, three different bulk flow structures. The air-methane mixture was obtained injecting the gaseous fuel into the inlet manifold varying its pressure and the injector position, either very close to the inlet valves, in order to obtain a stratified-like mixture, or more upstream, to obtain a homogeneous-like mixture. By combining the two different positions of the injector and the three air bulk flow structures, seven different inlet setup have been tested, at different values of engine speed and load.

The effects of several operating parameters on dual fuel combustion at light load were investigated by means of direct endoscopic observation of the process. Therefore, an intense experimental campaign was performed on a single cylinder diesel common rail research engine, converted to operate in dual fuel mode and equipped with optical accesses and variable intake configuration. Three bulk flow structures of the charge were induced inside the cylinder by activating/deactivating the two different inlet valves of the engine (i.e. swirl and tumble). Methane was injected into the inlet manifold at different pressure levels and varying the injector position. In order to obtain a stratified-like air-methane mixture, the injector was mounted very close to the inlet valve, while, to obtain a homogeneous-like one, methane was injected more upstream.

The influence of some injection parameters (as main injection timing, pilot injection timing, pilot injection duration) on noise emissions and combustion noise level of a Diesel engine has been evaluated. The noise emissions of an in-line, four cylinder, turbocharged FIAT 1929 cm3 TDI engine were measured using an ambient microphone and accelerometers. The injection system of the engine used was the high-pressure Common Rail system. The experimental results were elaborated using an ANOVA (analysis of variance) technique, to evaluate the influence of the control parameters on the controlled ones. Moreover, a multi-layer neural network was used to predict noise emissions and vibration level. It was found that the accelerometer mounted on the top of the engine bolt, which clamped the head of the cylinder to the crankcase, gave the best coherence of the results.

Modeling autoignition in diesel engines is a challenging task because of the wide range of equivalence ratios over which it takes place. A variety of detailed autoignition models has been proposed in literature for different fuels. Since these models include about one thousand chemical reactions and more than one hundred species, their application to CFD engines simulations requires a very high computational time, so that they are of no practical interest. In order to lower the computational time, a number of reduced models has been developed including the shell model, which is one of the most used. This model does not take into account low temperature kinetics and consists of seven reactions and three radicals. The use of this model in engine simulations shows its limits when applied to delayed injections because of the predominant influence of the low temperature kinetics. A modified version of the shell model is proposed in the present study.

The aim of the present work is to evaluate the influence of the pilot injection on combustion of a TDI Diesel engine for different engine torque and speed conditions. For this investigation, pilot injection timing and duration were varied on a wide range of values, and their effects on combustion pressure, rate of heat release, pilot and main combustion delay, combustion process and exhaust emissions in terms of NOx and smoke were analyzed. An in-line, four-cylinder, turbocharged FIAT 1930 cm3 TDI Diesel engine, equipped with Common Rail injection system, was tested. A piezoelectric sensor was located in the combustion chamber in order to acquire combustion pressure; from these signals, gross heat release rate was derived in order to analyze the combustion behavior. Pollutant emission levels have been measured by means of a gas analyzer, while for smoke an opacimeter was used.

The optimization procedure adopted in the present investigation is based on Genetic Algorithms (GA) and allows different fitness functions to be simultaneously maximized. The parameters to be optimized are related to the geometric features of the combustion chamber, which ranges of variation are very wide. For all the investigated configurations, bowl volume and squish-to-bowl volume ratio were kept constant so that the compression ratio was the same for all investigated chambers. This condition assures that changes in the emissions were caused by geometric variations only. The spray injection angle was also considered as a variable parameter. The optimization was simultaneously performed for different engine operating conditions, i.e. load and speed, and the corresponding fitness values were weighted according to their occurrence in the European Driving Test.

The effect of the shape of the bowl on the combustion process and emissions of a Natural Gas - Diesel dual fuel engine is analyzed. The simulation of the dual fuel combustion is performed with a modified version of the KIVA3V code where diesel is treated as the main fuel and a further reacting specie is introduced as methane (CH4). The auto-ignition of the pilot is simulated with a modified version of the Shell model and the first stage of the combustion, related to the pilot burning process, is simulated with the Characteristic Time Combustion model. When the temperature of the mixture reaches a certain threshold, a kernel of combustion is initialized. Until the kernel reaches a nominal radius the combustion of CH4 is prevented. The combustion of CH4 is simulated with a turbulent characteristic time too. Numerical models were chosen as a compromise between accuracy and computational time.

A 3-D analysis of the flow through a multihole, V.C.O. (Valve Covered Orifice) nozzle for D.I. Diesel Engine has been carried out. The analysis was performed by means of a finite element code. The nozzle comprises five injection holes. Aims of the analysis were: the investigation of the pressure drops along the conical clearance between the needle and the nozzle; the evaluation of the energy losses in the injection holes; the disclosure of the velocity profile at the injection hole outlets. the differences of flowrate for each hole with geometrical asymmetries. This kind of analisys is the first step of a more complete spray analysis; in fact, the spray from an injection hole is influenced by the injection pressure and the velocity profile. In particular, the needle lift and the needle tip deviation have been parametrized. The analysis betters both the theoretical knowledge of this kind of nozzle and the hydraulic phenomena occurring inside.

In the present study, the influence of pressure waves propagating in the ducts of common rail injection systems on engine out emission has been investigated. The pressure waves originated by the closure of the injectors are characterized by an amplitude that can easily be greater than 10 MPa. When a multi injection strategy is adopted such fluctuations can strongly affect fuel delivery rate of subsequent injections and therefore emission levels and fuel consumption. The paper reports the results of an experimental investigation that has been carried out on a single cylinder engine equipped with a common rail electronically controlled high pressure injection system and an optical access, via endoscopes, for the visualization of soot and combustion process. The used injection strategy consisted of pilot and main injection. To allow the start of the main injection on a local pressure peak or valley without changing injection timing, injection system ducts of different length were used.

A simulation model of an injection system for reciprocating engines has been developed to study the influence of the geometrical and mechanical configuration of the injection apparatus on the injection flow characteristics. The suggested model simulates pressure wave propagation in the pipelines, particularly in presence of cavitation, and injector behaviour. The model used for nozzle simulation evaluates fluid-dynamic phenomena in the nozzle sections and chambers. This allows prediction of injector geometry influence on the flow parameters and simulation of general behaviour of the apparatus and the spray using different nozzles (with sac, without sac, with reduced sac). Lastly, a model of the structure by a finite elements method allows the study of dynamics of the moving elements. The mathematical model has been verified through a series of experimental measurements. The comparison between numerical and experimental results has been satisfactory.

In the present investigation, a parametric study of the geometric characteristics of a two-cylinder four-stroke gasoline engine was carried out. Engine power, torque, specific consumption, engine efficiency, in-cylinder pressure for both the cylinders and pressure along the intake and exhaust manifolds at different positions were experimentally measured for engine speeds ranging from 5000 to 9500 rpm. All measurements were made under steady state conditions and full load. Engine characteristics were calculated by means of a 1-D model, which was used to calculate wave propagation in the intake and exhaust manifolds. A zero dimensional model was used to account for the in-cylinder phenomena. In the 1-D model the effects of pipe curvature, restriction geometry, gas friction, and heat transfer to the manifolds walls were considered. Numerical results showed good agreement with the measurements over the investigated range of operating conditions.

An analytical methodology to efficiently evaluate design alternatives in the conversion of a Common Rail Diesel engine to either CNG dedicated or dual fuel engine has been presented in a previous investigation. The simulation of the dual fuel combustion was performed with a modified version of the KIVA3V code including a modified version of the Shell model and a modified Characteristic Time Combustion model. In the present investigation, this methodology has been validated at two levels. The capability of the simulation code in predicting the emissions trends when changing pilot specification, like injected amount, injection pressure and start of injection, and engine configuration parameters, like compression ratio and axial position of the diesel injector has been verified. The second validation was related to the capability of the proposed computer-aided procedure in finding optimal solutions in a reduced computational time.

A new and unique four-stroke i.c. engine without the conventional crankshaft is described. A lobe plate, which moves the piston according to predictable laws of motion, transforms reciprocating movements into rotative ones. The idea derives from the observation of the structure and functioning of pumps with axial plunger whose units plungerod, moving, holds closely to a plate whose angle of inclination determins the motion characteristics and the value of the stroke itself. The new solution introduces a more efficient method of transferring power from a piston to a driveshaft. A peculiar configuration of engine block has been designed, in which pistons, purposely designed, transmit power to a purposely shaped disk. Each piston follows the shape of this disk during the revolutions. The cam provides a broad range of engine displacements using only one block, varying only the piston laws of motion according to the different disks used.

A mono-cylinder engine was built, because of its costs and the semplicity of designing, as flexible prototype. A scavenging system with four ports, two by two simmetrical, was chosen to respect the modern theory of scavenging optimization. The scavenging flow was supplied by a carter-pump; it has been used as first experimental solution. The prototype has been entirely realised and the following experimental measurements have been carried out: the pressure in combustion chamber, in carter pump, in pipes and injection system, as well as the fundamental parameters of engine functioning.