An internal combustion alternator with both free piston and cylinder

Abstract

The free-piston generator has more merits than the traditional reciprocating engines, and has been under extensive investigation. This study focuses on the development two novel perspective ideas unlike already advanced the linear free piston generator. These are: (1) to make both piston and cylinder free that provides ideally balancing of the system; (2) to turn from the linear scheme of a generator to rotary design because of simplicity and compactness. The mathematical simulation of operation of the linear two-stroke cycle alternator with both free piston and cylinder was conducted with using the model of zero-dimensional dynamics. Combustion of methane-air mixture with excess air ratio of 1.2 was considered. Both heat and friction losses were taken into account. Operation particularities of such system were analyzed. It was found that oscillation amplitude of moving parts did not exceed of 70 mm at frequency of ∼50 Hz for alternator with following basic parameters: cylinder bore of 80 mm, length of 400 mm, piston length of 120 mm. Mass of both piston and cylinder was chosen identical and equal of 3 kg. It was shown that the efficiency of the chemical energy conversion reached of 46%, and specific power was high as 40 kW/l at compression ratio of 40. The lab scale pneumatic alternator in rotor variant with both free rotor and cylindrical body was assembled for experimental demonstration of rotary design capability. The alternator was fed with compressed air of low pressure below of 6 atm. The electrical power in the load reached of 10 W at input power with intake compressed air about 100 W. The results indicate that alternators with both free piston and cylinder in linear and rotary designs have the potential to achieve high efficiency and provide the vibration – free operation.