QUOTE(the_catacombs @ Nov 7 2007, 12:13 PM)
jom jom... come melaka TT and discuss with me loh...
diesel engine doesnt have sparkplugs... when diesel+O2 mixture is compressed, the detonate easily... means under compression, diesel can detonate more easily compare to petrol.... while petrol, the higher its octane rating, the harder for it to detonate under compression... thats why petrol engines need a sparkplug to ignite the air/fuel mixture....
why me show u guys around??... i not local also...

actually,...diesel engines use glowplugs to start the engine going when it is cold
the diesel is not mixed with the oxygen and then compressed
the air is drawn into the cylinder and compressed
and then when the piston is at TDC (top dead center) the diesel fuel is injected into the cylinder
the temperature of the air is now very hot due to the compression (PV/T)
...this obeys the standard gas laws
the compressed air's temperature is higher than the diesel's flash point and thus ignites the fuel instantaneously upon injection
diesel has a higher flash point than petrol
which means petrol combusts more easily than diesel
i think the mistake u made here is that u failed to take into account the difference in the compression ratios of the two engines
diesel engines operate at a higher compression ratio
this is one of the reasons why it is more efficient as compared to a petrol engine
the higher the pressure and temperature the system works at (the further away it is from the heat sink and ambient values) the more efficient will a heat engine's operation be
petrol engines have spark plugs to ignite the fuel because the air fuel mixture is not compressed to a pressure which will cause the temperature to increase pass the flash point of the petrol
where as in diesel engines the air is compressed to a pressure which causes the air to pass the flashpoint of diesel so that when the diesel fuel is injected into the cylinder, the fuel spontaneously combusts
This post has been edited by neosaint99: Nov 7 2007, 10:55 PM