Electric energy balance of the Rotax 912 with fuel injection

A majority of ultralight aircraft is powered by the Rotax 912 ULS, which is a four-cylinder carburettor piston SI boxer engine. However, its power-to-power advanced aircraft is insufficient. This article discusses the examination of the Rotax 912 fitted with a modified power system and mechanical charging to increase the power of a base unit by 36%. This engine was developed as a collaborated project of the Lublin University of Technology and the AVIATION ARTUR TRENDAK & SON GmbH, a manufacturer of autogyros. Sources of energy in the Rotax 912 are generated with a generator integrated with an ignition system of a maximum power of 250 W at 5800 rpm and 13.5 V [1]. The technology of fuel injection and charging required us to apply control systems and to measure engine-operating parameters, which resulted in higher electric energy demand. Additionally, a mechanical pump was replaced with a more efficient electric pump, which also changed electric energy balance. The examination was conducted on the test stand of the Department of Thermodynamics, Fluid Mechanics and Aviation Propulsion Systems of the Lublin University of Technology. The measurement system consisted of the Tektronix TCP305 current probes and TCP A300 converters. Signals were recorded with data acquisition cards and the National Instruments Ni CompaktDAQ module. Power consumption was measured for the selected speed ranging from 2000 to 5800 rpm. The current probes were appropriately installed on power cords. The probes recorded respectively the power consumed by the fuel pump, the energy demand of the lambda sensor, and the electricity taken by the ECU. The data obtained was converted with the author's script in LabVIEW. Based on the results, the highest electricity demand shows the fuel pump. Furthermore, increasing engine speed and load results in higher pressure in the fuel system and consequently in the higher power demand of the pump. The pump consumes up to 89% of all energy consumed by the system. In the control system, the highest demand shows lambda sensor BOSCH LSU4.2 [4]. With the increase in speed, the exhaust gas temperature increases, which leads to less power consumed by the heater of the sensor head. The demand of the other measurement systems and actuators is less than 10.6% of total consumption. The investigation shows that the total power demand of this new system ranges from 63 to 73 W, which is from 24 to 70% of the total power output from a generator mounted on the engine.