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The developments of an open-chamber stratified-charge engine are herein described; the aim of this engine is to work at part-loads with low fuel consumption while remaining, however, under acceptable exhaust emissions. The essential purpose of this research has been to markedly amplify the overall air-fuel ratio field in which the engine working is regular. This also serves to modify the engine load by varying the air-fuel ratio instead of air throttling so that the corresponding losses can be avoided. By studying and setting up a proper injector, the fuel injection system has been considerably improved. In fact this injector gives a suitable spray geometry, with particular regard to the spray penetration, the spray angle and the droplet size. Injection pressure and timing have also been investigated in order to optimize engine performance.

Gasoline direct injection in two-stroke engines has led to even more advantageous results, in comparison with four-stroke engines, as far as unburned hydrocarbon emissions and fuel consumption are concerned. A new electronically controlled injection system has therefore been fitted in a crankcase-scavenged two-stroke engine, previously set up with indirect injection equipment. The comparison between the performance of the two gasoline feeding systems has highlighted the potential of the direct injection strategy. The direct injection system here tested has allowed the optimization of the engine torque characteristic at wide open throttle operating conditions. Moreover, the engine original exhaust system, has been replaced with an expansion-chamber exhaust-pipe system, in order to evaluate the impact of direct gasoline injection also with these optimized exhaust configuration.

An original 2-stroke prototype engine, equipped with an electronically controlled gasoline direct-injection apparatus, has been tested over the last few years, and the performances of these tests have been compared with those obtained using a commercial crankcase-scavenged 2-stroke engine. Very satisfactory results have been obtained, as far as fuel consumption and unburned hydrocarbons in the exhaust gas are concerned. Large reductions in fuel consumption and in unburned hydrocarbons have been made possible, because the injection timing causes all the injected gasoline to remain in the combustion chamber, and thus to take part in the combustion process. Moreover, a force-feed lubrication system, like those usually exploited in mass-produced 4-stroke engines, has been employed, because of the presence of an external pump. In fact, it is no longer necessary to add oil to the gasoline in the engine, as the gasoline does not pass through the crankcase volume.

An electronic instrument for the measurement of fuel consumption in reciprocating internal combustion engines for light aircraft has been designed, manufactured and tested. The operating principle of the measuring device is based on the simple, theoretically supported and experimentally verified observation that the fuel mass flow rate is almost exactly proportional to the product of the intake manifold air pressure “pc” and the engine revolution speed “n”. Therefore, only two sensors are needed, and no fuel pipe cutting is required for installation and operation. This feature represents a major point in favor of simplicity, reliability and safety. The aim of the instrument is to provide a fuel consumption indication which can be used during cruising. The instrument is not intended as a replacement for the usual on-board fuel level gauge, but can be used to integrate the flight information with the overall and instantaneous fuel consumption data.

The influence of injection pressure on the performance of a FIAT passenger car Diesel engine prototype equipped with a Common Rail Fuel Injection System has been investigated. An increase of the injection pressure from 1300 up to 1500 bar, during this research, has permitted the assessment of the effect of this parameter on the maximum power and on the smoke emissions. The tests were performed at 4000 rpm, with an equal mass of injected fuel. The influence of the injection advance has also been taken into consideration during this experimental analysis. The in-cylinder pressure was first detected and recorded, together with the brake torque and emissions; the in-cylinder pressure was then used for the determination of the principal combustion characteristics, on the basis of the heat release analysis. Finally, higher injection pressure could be used as an effective parameter to increase the maximum power angular speed.

Experimental tests have been carried out on a single-cylinder crankcase-scavenged two-stroke engine, with both indirect and direct gasoline injection, in order to compare the results obtained with these two different fuel-feeding systems. Engine operating conditions were chosen like those of a typical aeronautical application. They were determined using a theoretical method, that is by computing the power of an aircraft, that is necessary for a steady-state flight at different aircraft velocities. This power curve turned out to be in good agreement with the “propeller load” that was experimentally found through preliminary bench tests, that is, the cubic characteristic, of power versus engine revolution speed, matching the maximum power of the engine. Brake specific fuel consumption (bsfc) and exhaust emission measurements were then carried out using bench tests along the “propeller load”.

The aim of this work was to obtain a reduction in pollutant emissions, in particular for NOx and Soot, in an “Off-Road” DI Diesel Engine, equipped with a common rail injection system, by means of exhaust gas recirculation (EGR). First, an engine simulation was performed using a one-dimensional code, and the model was then calibrated with experimental results obtained from a previous research work conducted on bench tests. Thanks to the engine model, specific emissions were then determined in all conditions, that is, in “eight modes” pertaining to engine loads and speeds. Both the injection advance and EGR amount were changed for all of these conditions in order to obtain the best compromise between fuel consumption and emissions and to respect standard regulations. The investigation was performed using both the Wiebe and a more complex combustion models; this latter allows in fact to determine the soot emission through the Nagle-Strickland model.