Sleeve Valve Engine
The sleeve valve engine was developed by Ricardo prior to World War II and were used during the war for high output spark ignition aero engines.
In the sleeve valve engine the conventional valve train was replaced by a ported cylinder liner that was then rotated to align with ports in the block so as to achieve the timing for the intake and exhaust strokes for the four-stroke cycle. The cylinder head gasket was replaced by rings that allowed the cylinder to be sealed to the head and still allow the cylinder to rotate.
The aim was to remove the hot exhaust valves thus reducing early detonation of the fuel air mix allowing higher operating pressures and thermodynamic output.
It is of interest to note that the mechanical friction of this system was lower than a conventional engine. This is attributed to the rotary motion in the cylinder reducing friction with the piston. In addition the cylinder bore wear is also reduced with the rotating cylinder.
The claims of the sleeve valve engine over a conventional poppet valve engine do not appear to have been backed up with measurements.
Reference [Raymond] lists the following points with regards to the sleeve valve:
- The sleeve must be as thin as possible and have a high thermal conductivity as the sleeve and additional oil film on the outer surface are a further barrier to the removal of heat from the piston.
- The coefficient of expansion of the sleeve has to be a good match to that of the cylinder barrel.
- The sleeve material had to be compatible as a bearing surface with the piston, rings and cylinder barrel with marginal oil film conditions.
- The sleeve has to be machined to very high levels of roundness on both inner and outer surface.
The high level comparison between sleeve and poppet valve aero engines shows:
- Weight - sleeve valve engines were heavier than the equivalent poppet valve engine. Size - the frontal area (important in aircraft design) was equal in both designs.
- The air cooled sleeve valve engine had a significant advantage over the poppet valve engine with regards to detonation limited IMEP.
- Volumetric efficiency - the sleeve valve engine did not offer any advantage over the poppet valve engine.
- Friction - the sleeve valve engine resulted in lower friction.
Robert J. Raymond, "Comparison of Sleeve and Poppet-Valve Aircraft Piston Engines", Aircraft Engine Historical Society, 2005