Increase of compression ratio from 9.8 to 14 at a 100cc engine requires a reduction of the compression volume from 11.36cc to 7.69cc. If there is a standard Bajaj engine used, the bore is 53mm. In this way, milling distance at the cylinder should be about 1.67 mm. This is possible in general, but the timing chain guides have to be modified too (for test bench purposes, the timing chain guides can be modified; for mass production it is better to design them new). It is important to check the clearance of the valves in relation to the piston. Eventually, some bags have to be milled into the piston to avoid clash.

A second possibility includes the design of a new piston to provide a suitable shape of the combusion chamber. This requires the production of a new piston, which is more costly, but with a new piston design the combustion chamber shape can be optimmized according to the requirements of an effective combustion process with ethanol.

Kind regards,

Mario

Thanks for answering the question.

The bore of our engine is 47 mm , and the compression volume is 10.725 cc. 

Does piston's head design play any role in creating turbulence for air-fuel mixture which might help in efficient combustion ? Additionally , what do you mean by the sentence - ' Eventually, some bags have to be milled into the piston to avoid clash.'?

Yes, if the bore is 47 mm, the value for machining the cylinder is 2.12 mm. Of course, piston design influences turbulences in the combustion chamber and plays a role for efficient combustion. The attached figure shows an example for bags in the piston upper surface, that avoid collision of pistion and valve during valve opening phase.

Kind regards,

Mario

Thank you. @Mario Sir , could you please tell me some reference books / links for material on the same topic? 

Modifying cylinder to reduce clearance volume

design of combustion chamber as whole mainlly depends upon the shape of piston. then, you can modify the shape of piston crewon to get the required compresion ratio,

@M A Kalam Sir, modifying the cylinder would also require us to modify other parts of the engine block like the connecting rod etc. How can we go about the procedure?

@Mahmoud Sir , we need a reduction in our engine's clearance volume. There is not much of a gap between the cylinder head and the top of our piston when it is at the TDC. How could we go about modifying it?

Added metal to the piston head : should not be any problem with the connecting rod. But engine cc is very small, increasing CR to 14 will affect on ignition.