There should be no abrupt changes in pressure in the cylinder. Under certain conditions, the last portion of the unburned mixture ahead of the flame front will ignite spontaneously and then burn very abruptly, resulting in shockwaves that produce an audible knock. This knocking or pinging can be caused by low octane fuel, combustion chamber deposits, or a poor cooling system. Some light pinging is acceptable, but heavy knocking indicates a potential problem. To test the antiknock index of gasoline, the Bureau s lab is equipped with large octane test engines.
Gasoline is formulated differently for varying climate conditions.
As weather gets colder manufacturers bring the initial boiling point down to help cold engines start easier, however, this lower initial boiling point would encourage some pinging in warmer weather and it is therefore raised as seasons warm. In order to help with deposits and emissions the final boiling point of gasoline is kept to below 437 degrees Fahrenheit. The Bureau tests the boiling points of fuel to ensure the gasoline being sold throughout the State has the correct formulation for the season. Other tests performed examine the vapor pressure, sulfur content, oxygenated compounds of the gasolines. Diesel is formulated from this mixture of larger hydrocarbons and is therefore much more oily and viscous.