Fuel — performance characteristics (Nissan Murano Z50)

The performance characteristics of gasolines are determined by the requirements for detonation resistance and fractional composition. Engine detonation is determined by the spontaneous ignition of the portion of the fuel-air mixture that is farthest from the spark plug. The external manifestation of detonation is the presence of ringing metallic knocks, which are caused by the multiple reflection of shock waves from the walls of the combustion chamber. The detonation resistance of gasoline is assessed by its octane number. The octane number of gasoline is determined by the motor or research method, with the motor method better characterizing the anti-knock properties of gasoline under conditions of forced engine operation, and the research method - under conditions of engine operation in the urban cycle, i.e., when the engine operates at a relatively low crankshaft speed with frequent stops. If the octane number of gasoline is determined by the research method, then the gasoline marking contains the letters AI (AI93), if motor octane, then only the letter A (80).

To increase detonation resistance, antiknock agents are added to gasoline.

Caution: The use of leaded gasoline in cars with an engine with electronic injection is unacceptable, as it leads to failure of the lambda sensor due to clogging of the working volume of the sensor with lead. In this case, the on-board computer will not be able to control the system, and the engine will stop working. For a similar reason, leaded gasoline cannot be used in vehicles with a catalytic converter. Of course, a catalytic converter failure will not have such serious consequences for the car, but the toxicity of exhaust gases will increase.

The main design factor that determines an engine's octane requirements is the compression ratio. Increasing the compression ratio allows for increased engine power and reduced specific fuel consumption, but with an increase in the compression ratio it is necessary to increase the octane number of the gasoline used. Using gasoline with a lower octane number causes detonation and increases the wear of engine components (destruction of bridges between piston ring grooves, burnout of the cylinder head gasket, burning of valves, etc.). When using gasoline with a lower octane rating for a short time, driving with sudden changes in crankshaft speed is not allowed; lower gears should be used primarily.

Domestic gasolines (except for AI98 gasoline) are available in two types: winter (it is recommended to use it in most of the country from October 1 to April 1) and summer(from April 1 to October 1). Using summer gasoline in winter creates difficulties with starting the engine, increasing losses in dynamics and accelerating wear of engine components. Heavy fractions of gasoline, which have high final boiling points, do not have time to evaporate in the intake system and enter the engine cylinders in liquid form; some of them do not have time to burn, and engine efficiency decreases. Unburned fuel is deposited on the cylinder walls in the form of carbon deposits, increasing engine wear. Carbon deposits also form when using high-quality gasoline during frequent urban driving on an unheated engine. In this case, periodic runs at high speed outside the city are useful - this burns out the accumulated carbon deposits.

(Information copied from the website: nissanbook.ru)