Q & A > Question Details
For a given gasoline car or bike (engine), does the efficiency increase by increasing the fuel RON? i.e., without changing the engine does the efficiency increase by just increasing the RON of fuel.
03/04/2019 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Octane number (RON) is a measure of antiknock properties of the fuel. When RON of the fuel is high or increased based on requirement there can be homogeneous combustion process without any knocking. . If the combustion process is homogeneous it completes the power cycle i.e completes every two crankshaft revolutions as a function of every four stroke engine efficiently or without loss of power.
02/04/2019 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Octane Number is an indication of the combustion intensity {heat and pressure inside the combustion chamber during combustion) a gasoline will permit before harmful detonation (knocking) will happen.
For a given engine design the maximum power output is NOT increased by increasing the fuel 'octane number' above that required to avoid detonation. However, some engines will produce more power if ignition timing is advanced somewhat, and this increases the fuel octane number needed.
Current automotive engines and carefully designed and adjusted for maximum fuel efficiency at all times by continuously adjusting the ignition timing and fuel to air ratio. The engines are equipped with 'knock sensors, which detect detonation and reduce the ignition timing just enough to prevent knocking (detonation.) This results in maximum obtainable efficiency at those conditions of load, atmospheric conditions, etc.
With continuous knock sensors, some new engines will develop more power from higher octane fuel as this allows the ignition timing to be advanced and power increases. This does not necessarily increase fuel efficiency however.
Fuel efficiency is determined more by 'compression ratio' and engine operating temperature.
Nissan Motors has developed and is selling cars that vary the compression ratio to maximize power and fuel efficiency continuously with different fuel octane number. A higher fuel octane number WILL allow higher fuel efficiency if the compression ratio is increased to optimize the fuel efficiency. New instrumentation and computer control technologies are able to measure more precisely and adjust fuel flow and compression ratio for the required power output.
Maximum economic efficiency is achieved by using the LOWEST octane fuel that works in your driving without excessive knocking. Light (or trace) knocking is the most fuel efficient operation.