The "hit and miss" method of governing internal combustion (I.C.) engines was a popular speed control mechanism used in early stationary engines (late 19th to early 20th century). Unlike modern throttle-governed engines, hit-and-miss engines controlled speed by intermittently skipping ignition cycles rather than reducing fuel intake.
How Hit-and-Miss Governing Works:
Governor Mechanism – A weighted centrifugal governor (usually flyball-type) is linked to the engine's throttle or ignition system.
Speed Regulation – When the engine runs above the set speed:
The governor disengages the exhaust valve mechanism, preventing the next power stroke.
The engine "misses" a firing cycle, slowing it down.
Resuming Operation – When speed drops below the set limit:
The governor re-engages normal operation.
The engine "hits" (fires) on the next cycle.
Advantages of Hit-and-Miss Governing:
✔ Simple & Reliable – Fewer moving parts than throttle governing.
✔ Better Cooling – Skipping cycles allows engine to cool slightly between firings.
✔ Fuel Efficiency – No wasted fuel during "miss" cycles (unlike throttled engines, which constantly consume fuel).
Disadvantages:
✖ Uneven Power Output – Speed fluctuates more than with throttle governing.
✖ Noisy Operation – Distinctive "pop-pop-pop" sound due to intermittent firing.
✖ Not Suitable for Variable Loads – Best for constant-load applications (e.g., water pumps, sawmills).
Comparison with Throttle Governing:
| Feature | Hit-and-Miss | Throttle Governing |
|---|---|---|
| Speed Control | Skips cycles | Adjusts fuel-air intake |
| Efficiency | Better at light loads | Less efficient at low loads |
| Complexity | Simpler | More complex carburetion |
| Applications | Old stationary engines | Modern engines |
Legacy:
Hit-and-miss engines are now mostly obsolete, replaced by throttle-governed and electronic fuel-injected engines. However, they remain popular among antique engine collectors and are still seen in historical demonstrations.
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