Search Results

With this paper the author first of all wants to honor the memory of Professor Alberto Morelli with whom he had the privilege of working for many years at the Politecnico di Torino. Morelli radically changed the way of designing car body shapes, while bringing the aspect of reducing the aerodynamic resistance of a vehicle to the attention of car designers. Morelli’s research activity began in the early 1950s and, between the 1950s and 1960s, he designed and built a number of car prototypes, whose coefficient of aerodynamic resistance was substantially reduced compared to that of the cars of that time, sometimes resorting to revolutionary architectures such as a “diamond” arrangement of the wheels. A fundamental step of Morelli's research in the field of vehicle aerodynamics was the Pininfarina full-scale wind tunnel project, which was set up between the end of the 1960s and the beginning of the 1970s, and was inaugurated in 1972: fifty years have therefore passed since that occasion.

As in the standard American Society for Testing and Materials (ASTM) procedure which is used to evaluate the fuel Octane Number (ON), some signal properties are considered, while others are neglected, it happens that different pressure signals of the sensor, obtained from different fuels and operating conditions, can lead to the same Knock Intensity index (KI) value, even though the knock behavior is not the same. Therefore the aim of this work was to analyze the standard signal processing chain of the Cooperative Fuel Research engine (CFR) (from the pressure sensor to the knock-meter display) and its effects on the value of the KI, for different fuels and operating conditions.

Preliminary bench tests have been carried out on an original-design 2-stroke single-cylinder prototype engine, which is equipped with an electronically controlled gasoline direct injection apparatus. The main design and operating features of the engine concern: a unidirectional airflow during the scavenging process (from the inlet ports near the BDC to overhead cam-actuated valves), an external air pump (a Roots volumetric type driven by an electric motor) and a force-feed lubrication system, like those usually exploited in mass-produced 4-stroke engines. Experimental bench tests were carried out under low load, intermediate rotational speed operating conditions. The performances were compared to those obtained from a commercial crankcase-scavenged 2-stroke engine using an indirect injection fuel feeding system. Encouraging results were obtained as far as fuel consumption and pollutant emissions are concerned.

The aim of this study was to find a convenient set-up for an innovative engine dedicated to light aircraft through a numerical one-dimensional simulation. Six different engine layouts were analyzed in order to find the highest power/weight ratio and the least voluminous configuration. The first was a four cylinder, four stroke, horizontally opposed, naturally aspirated, water cooled engine with 16 valves that delivered 75 kW (∼100 bhp) at 2400 rpm for an estimated weight of 65 kg. A gearbox was also used in the naturally aspirated model to decrease the displacement, the weight and the overall dimensions. The other solutions involved these two engines in a turbocharged layout in order to gain a further downsizing. The supercharging was obtained through a centrifugal compressor driven by an exhaust-gas driven turbine, which also allows the power to be restored at cruising altitude.

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 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.