The internal combustion engine (ICE) is a type of heat engine in where combustion process in fuel occurs for an oxidization in a chamber that is an integral part of the system.
Theory acually said that the smallest engine runs on Single Atom. The nano engine can work like as used by the first using tiny electrodes in a cone of electromagnetic energy. The principle of the engine can be built all about ion .
As per the sources, the smallest 4 stroke spark ignition engine was built at NewYork by Georg Luhrs.
Here we have some collection of smallest IC Engines which are built for different applications such as model.
1. World Smallest Hand Small Engine:
The engine is with displacement of 44cc and length of 5 inches.This engine starts using hand lever which you need to rotate 3-4 times then it starts cranking .
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2. Tiny V 12 Engine
Image Source : i.pining
3. Ronald Valentine's Combustion Engines
4. Tiny V8 Engine
Image Source : craftsmanshipmuseuum
Image Source : i.ytimg.com
The mini engine was designed to run on liquid hydrocarbon fuels such as butane or propane, chemical cousins of gasoline. One fluid ounce of fuel that will keep the motor running for two hours. Once it is optimized, the tiny engine will be able to run 10 times longer than a conventional lithium ion battery.
The motor and fuel can together weigh only a fraction of the weight of a standard battery which is same as used in a digital camera.
Also you must be curious to see the smallest crankshaft used in the IC Engine .
Image Source : mooregoodink