Increasing Reliability of a Small 2-Stroke Internal Combustion Engine for Dynamically Changing Altitudes

Remotely Piloted Aircraft (RPA) typically utilize commercial internal combustion engines (ICE) as their power sources. These engines are designed to run at sea level, but these aircraft are often pressed into service at higher altitudes where the performance characteristics deteriorate. A Brison 95cc two-stroke engine's performance characteristics at altitude are investigated using a test facility that can measure these characteristics over a range of pressures and temperatures. With its stock carburetor at sea level static (SLS) conditions, the engine makes 5.5 peak horsepower (hp) and brake specific fuel consumption (BSFC) ranged from 1.2-4.0 lb/(hp-hr). At 10,000 feet conditions, the peak hp drops 40% while off peak hp conditions can see a drop of over 90%. In addition, the carburetor makes operating at high altitudes unreliable. To increase reliability, a throttle body fuel injection (TBI) system was installed on the engine in place of the carburetor. The fuel injection system matched carburetor peak power at SLS conditions while increasing power by as much as 90% at low RPM and high altitude operating conditions. BSFC is decreased to a consistent 1.0 to 1.2 lb/(hp-hr) across all operating conditions. Lastly, both reliability at high altitude and startup reliability are increased with the TBI system while eliminating the need for tuning by the end user. The original document contains color images.