Expert: Paul Soderman - 4/13/2002

Question
What tern was given for measurement of quality of petrol

What sort of engines are 4 stroke, 2 stroke and jet.

Answer
I'm not sure what you mean by quality.  Heat value is most likely what you mean.  It is measured in BTU/lb (British Thermal Units per pound or joules/kg (better).  There are also various chemical qualities such as octane rating, type, etc.

Stroke refers to the number of movements of a piston in one combustion cycle.  A four stroke engine piston drives down on combustion, up to clear the exhaust, down to fill the chamber with fuel and air, and up for compression and combustion.  A two stoke engine piston drives down on combustion and up to clear the exhausut, fill the chamber, and combust.

A jet gets thrust from the combustion of fuel mixed with air that is allowed to expand and exhaust out a nozzle.