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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.

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.

As more stringent emission limits and low consumption requirements also involve s.i. 2-stroke engines, one of the most important design modifications that can cope with these constraints is to perform the scavenging process using pure air, which means not only fuel-free air but also oil-free air. A new single-cylinder prototype engine, equipped with a gasoline direct injection (GDI) apparatus has therefore been designed and built. In order to reduce manufacturing costs, this prototype was obtained by modifying a mass-produced 4-stroke 4-cylinder automotive engine. Apart from the replacement of the original indirect fuel feeding system with GDI, two more remarkable features should be pointed out: the use of a force-fed lubrication system, like those used in current 4-stroke engines and, as a consequence, the use of an external scavenging pump.

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”.

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.

An original instrument for fuel consumption measurement in reciprocating internal combustion engines for light aircraft has been developed and built. It is based on the detection of two parameters: the engine rotational speed and the manifold pressure. The aim of the instrument is to provide a fuel consumption indication which can be used during cruising. The instrument is not intended to replace the usual on board fuel level gauge, but can be used to integrate the flight information with the overall and instantaneous fuel consumption data, and with the cruising range indication, leading to a significant increase in flight safety. Some results of fuel consumption measurements from experimental tests are here presented and discussed. Such results were first obtained with the instrument installed on the engine during bench tests.

The performance of two-stroke spark-ignition engines is greatly influenced by the scavenging process The variation of the crankcase clearance volume has here been investigated as a method for engine-load reduction. This method allows the reduction of the load without throttling or only by partial throttling with a theoretical increase of the engine efficiency. A comparison of two methods (air throttling and crankcase clearance volume variation) has therefore been carried out. The reduction of pumping work, due to the use of the variable crankcase clearance volume, has not always caused a consequent reduction of the specific fuel consumption. This is mainly due to deterioration of the scavenging process and to the occurrence of pre-ignition which occur above all at light loads.

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.

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.

This work has been carried out on a two-cylinder s.i. automotive engine and it investigates spark advance, air-fuel ratio and variable valve overlap for low emissions and low fuel consumption, with an acceptable cyclic irregularity under idle conditions. An original application of a variable valve timing system, based on a passive electro-hydraulic link, has been used for this purpose. The instantaneous engine speed and in-cylinder pressure have been measured and recorded by means of an acquisition data system that allows both the determination and the comparison of some cyclic irregularity indexes, under different engine settings, at idle. The optimum spark advance, air-fuel ratio and valve overlap, which yield the best compromise between fuel consumption and cyclic irregularity, under idle operating conditions, have therefore been pointed out.

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.

This investigation was performed with the purpose of comparing the arodynamic drag of an automobile as measured in a full-scale wind tunnel with the drag as measured on the road. A definition of the drag coefficient as measured both on the road and in the wind tunnel is given in advance in order to allow a comparison to be made between the two operating conditions. Three medium size european cars were selected, one notch-back type and two hatch-back types. Road testing was mainly based on the coast-down method. The total resistance was determined by statistical analysis of the experimental results. The theoretical basis and the specifications of the procedure are investigated and justified. Additional outdoor and indoor tests were carried out in order to isolate the aerodynamic drag. The wind tunnel tests were conducted on the same cars fully equipped as tested on the road and in the same speed range.