Quote:
Originally Posted by aerohead
theunchosen,I'm relying on memory going back to the 1970s,with my I.C.Engine Lab class.While "ping" was acceptable under load,"knock" was considered dangerous to the engine and is the reason for anti-knock additives in gasoline,as tetra-ethyl lead,Methyl Tertiary Butyl Ether,and Ethanol.Engine manufacturers will recommend an octane rating for a particular engine to protect it from the knock caused by detonation which is created by a non-uniform flame front propagating from the spark source.The octane helps guarantee "controlled" combustion at maximum spark advance,allowing the engine to achieve peak efficiency for its compression ratio.
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Ping and knock are the same thing. Ping is one of its forms because it can be defined partially as a certain frequency that occurs in the engine. In that term it refers to a very short area with a very high output, the term also fits things like sonic-resonance where you ping the ground with a high frequency and listen for the ripple waves to come back. Lately the term more than most anything means a networking event in which a computer sends a packet that immediately returns after arriving to determine how much disconnect is between the two computers or however many machines or whatever array of machines.
Knock denotes what who was it . . . you also referred to as piston-slap for its tendencies to occur traveling out from the spark plug at the fringes of the system but almost always against the piston head itself.
knock/ping/piston-slap whatever is detonation. The knocking or the pinging don't cause the detonation. The jerk to the piston-driveshaft-trans-wheels-diff-whatever else comes because of that pulse emitted from the "instantaneous" conversion of fuel-air to CO2+heat+water+small amounts of other stuff.
All knock is detonation, but logic does not mandate that all detonation is knock. Such is the case here.
Fuel manufacturers are avoiding the fuel detonating during compression. Those compounds increase the amount of energy it takes to ignite the fuel, normally in open air this is bad. This is not open air though and the fuel-air is almost achieving its activation energy during the compression stroke so it just takes a little zap to make the ignition flame kernel start and expand. The activation energy would be a waste to burn it in open air because the fuel is then having to overcome that additional AE for no reason, but since its going to be compressed and we are going to add that enthalpy anyway, it doesn't hurt the cycle.
I believe the op is driving a Honda Jazz/Fit. Since the fit has anti-knocking ability its moot, but its not a very high power-weight engine so its not going to hurt his engine very much at all for ping to occur unless he runs it for say an hour under knocking. Then whats very likely to happen is something inside that engine is likely to outpace the cooling systems and pre-ignite destroying his engine. If that happens he will know because the engine's check light will come on and it won't accelerate properly at all and it will rev low at idle.