The primary criterion for selecting a car is the compression ratio of the engine, which is also the core energy saving index of contemporary cars.
The operation of the engine is composed of the cycle of “inspiration-compression-combustion-exhaust-inspiration” of the cylinder. The ratio of cylinder volume at the furthest point of the piston’s stroke to that at the nearest point is the compression ratio.
The cheapest and most effective way to reduce fuel consumption is to increase the compression ratio of the engine.
Increasing the compression ratio only changes the piston stroke. The more compressed the mixed oil and gas is, the greater its combustion reaction will be and the more fully it will burn.
But the compression ratio is not easy to move, because there has to be another index, that is, the knock resistance index, also known as octane, that is, the gasoline label.
The number of gasoline determines the point of detonation sooner or later, in fact, is to determine the power of the engine.
The knock resistance of fuel varies with its composition.
The higher the knock resistance of fuel, the higher the compression ratio of the engine may be, and the economy and power of the engine will be improved.
It IS DIFFICULT TO DETERMINE THE KNOCK RESISTANCE OF A FUEL BECAUSE IT DEPENDS NOT ONLY ON THE NATURE OF THE FUEL, BUT also ON THE type of engine, AIR-fuel ratio, cooling water temperature, intake temperature, ignition advance Angle, valve timing and so on.
In order to evaluate the knock resistance of fuel, two methods are generally used: motor method and research method.
The evaluation is generally carried out on a specially designed single cylinder engine with variable compression ratio.
According to the motor method, the test conditions are as follows: inlet temperature 149¡æ, cooling water temperature 100¡æ, engine speed 900 R /min, ignition advance Angle 14¡ã~26¡ã before TDC.
During THE test, WORK WITH THE measured fuel and gradually change the compression ratio until the standard knock strength is indicated on the detonation meter.
Then, keep the compression ratio and other conditions unchanged, switch to standard fuel work.
The standard fuel is a mixture of the highly explosive isooctane C8H18 (rated 100 octane) and the explosive n-heptane (rated 0 octane).
The ratio of isooctane to n-heptane is gradually changed until the deflagration intensity produced by the standard fuel is the same as that of the fuel under test.
The volume percentage of isooctane contained in the standard fuel is then the octane number of the fuel under test.
High octane, fuel shock resistance is good, on the contrary, the resistance is poor.