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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.

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.

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.