Performance Scaling and Measurement for Hydrocarbon-Fueled Engines With Mass Less than 1kg

Flight Test Results for a Fuel Cell Unmanned Aerial Vehicle

“…Still the fuel to rotational energy efficiency of the fuel cell powerplant is 29% (in terms of hydrogen HHV) at cruise. Again, this compares favorably to an efficiency of 13% for a 500W, 2-stroke combustion engine (in terms of the HHV of octane) [11]. The fixed pitch propeller requires a compromise between the propeller efficiency during low speed climb and during cruise.…”

Personal power systems

“…chainsaws) also represent commercially available and reliable personal power devices with high output capability. Cadou et al [96] surveyed 200 engines with mass below 1 kg and found that the power-to-weight ratio is nearly constant across a wide range of engine sizes, with 2-stroke engines having slightly higher performance than 4-stroke models.…”

“…With even rudimentary heat losses included in the scaling, however, it can be shown that the improvement in power density with decreasing size effectively terminates at characteristic dimensions around a millimeter [95]. Furthermore, as Cadou et al [96,97] has demonstrated, the promise of the cube-square law is not realized in practice at all, as the performance of small-scale engines does not increase with decreasing scale. In addition to the combustion challenges mentioned above, performance also degrades because of increased friction, reduced turbulent mixing, higher viscous drag, combustion wall quenching, and sealing inefficiencies, among others.…”

“…Power output of 2-stroke and 4-stroke engines weighing less than 1 kg. Solid symbols correspond to existing engines while open symbols correspond to engines in development [96]. Used with permission.…”

“…The existence of liquid films in full-size automotive engines is problematic because films can lead to lower fuel economy, higher soot emissions, and increased deposit formation. Further diagnostic intervention is required to confirm if these same effects occur for the mesoscale, but such investigations are beginning to develop [93,96,97,163].…”