Aplicação de metodologia de projeto para desenvolvimento de motor para aeronaves experimentais

Abstract

Internal combustion engines have been the subject of constant changes and improvements to reduce fuel consumption and emissions of polluting gases. In experimental aviation, the goal is to use smaller engines with high power density and high efficiency. In this context, this thesis presents the technological development of a new concept two-stroke engine, with a uniflow scavenging system, flathead valve arrangement, spark ignition, and avgas fuel for application in experimental aviation. The design methodology was divided into three parts: i - Engine concept (from concept to digital mockup, including 1D and 3D CFD simulations); ii - Prototype manufacturing design; iii - Experiment design (proof of concept). The developed engine concept features a single-cylinder configuration, lubrication via the crankcase, port fuel injection, supercharged, classic uniflow intake ports, and an exhaust valve arrangement parallel to the cylinder (flathead system). The technical specifications define a piston diameter of 70 mm, a stroke of 66.2 mm, resulting in a displacement volume of 248 cc, with an effective compression ratio of 7,9:1, a maximum speed of 3000 rpm, allowing for direct coupling of a propeller to the crankshaft. The 1D and 3D (CFD) simulations showed a power output of 23 kW at 3000 rpm, torque of 77 N.m at 2700 rpm (cruising speed), and an efficiency of approximately 31%. The results of the experimental tests for the prototype's proof of concept showed a power output of 10,5 kW and torque of 63 N.m at a speed of 1600 rpm, indicated specific fuel consumption of 465 g/kW.h, but with low efficiency, approximately 18%. These results allow us to conclude that the presented concept is technically feasible. The excessive cylinder scavenging prevented the engine from speed above 1600 rpm, leading to low efficiency. However, this condition can be addressed through adjustments in the valve timing and the opening (timing and position) of the intake ports. Therefore, this study represents advancements in the field of internal combustion engines for use in experimental aviation.