goodvibes

its late ,im tired and have to get up at 5 inthe morning,but its time to initiate anyone who likes to learn , some little known secrets about how engines really work,but first,
well done, yes diesel has about 8 percent advantage re energy density and probably burns at a higher temp, havent looked into that one, but this dont explain the massive advantage in mpg and incredible
increase in torque at tickover speed that the diesel has.
i live on a steep hill but my peugeot 1527cc will pull away in first gear effortlessly without touching the accelerator and with a run up will climb this hill in 3rd gear, still at tickover speed, why? [ sorry about talking nonsense again] because there is no restriction on the amount of air that the engine is try ing to 'suck' in.
so, the ACTUAL compression ratio will be close to the mathematical one of about 22 to1 , in other words
if the engine was a 4 litre the induction stroke would pull in almost 1 litre of air at roughly atmospheric pressure an d cram it into the tiny combustion chamber of 1 divided by about 22 of a litre, loads of compression, lots of torque all at tickover, and all achieved at minimum fuel injection.
but , what would happen if we,' throttled' the air intake like a petrol engine? simple to find out, just remove air filter and fit a carburettor from a 1500 car to the manifold intake. now temporarily jam the throttle wide open and drive,you wouldnt notice any difference , a 1500 diesel will suck in roughly the same amount of air as a 1500 petrol,but now unjam the throttle and jam it in the 'idle' , tickover position.
id be amazed if the engine continued to run, why? because with the throttle shut' and 'idle' speed of about 1000 rpm the cylinder has only roughly[ im tired]30 thousands of a second , top dead centre to
bottom dead centre to 'suck' in 1litre,roughly' of air, if youve ever looked into a carburettor intake at
idle position the actual gap between the throttle disc and intake tube probably equates to the area of a drinking straw, ever tried breathing through a straw? how the hell can 1litre of air be sucked through the equivelant area of a straw in 30 milliseconds?, the answer is, IT CANT, by the time the piston reaches bottom dead centre ,there will be a PARTIAL VACUUM in the cylinder , exactly the opposite of what we want, as the piston travels up on compression stroke the partial vacuum will decrease , eventually reach atmospheric and by the time tdc is reached, it might actually reach a low compressio ratio .
im hammered its almost time to get up, but in a nutshell its very high compression ratios that produce good torque for small fuel input, this can only happen with throttle wide open or no t hrottle at all[diesel],
the petrol engine is aVARIABLE COMPRESSION ENGINE because the throttle, unless its wide open,prevents the cylinders from filling up with air at atmospheric pressure ,producing lousy' volumetric efficiency,' [look it up]
you may be right about some one not knowing what their talking about, but im happy to let others decide which one of us that is.
im asleep,
mike.