The Wankel engine has the advantages of compact design and low weight over the more common internal combustion engine, which employs reciprocating pistons. These advantages give rotary engine applications in a variety of vehicles and devices, including automobiles, motorcycles, racing cars, aircraft, go-karts, jet skis, snowmobiles, chainsaws, and auxiliary power units. Certain Wankel engines have a power-to-weight ratio over one horsepower per pound. Most engines of the design are of spark ignition, with compression ignition engines having been built only in research projects.