Auto ignition
Auto ignition
(OP)
Hello everybody,
While I was browsing the web, I came across something that makes me wonder. the auto ingnition tempreture of gasoline is higher than diesel, then why is compression ratio in a gasoline engine less than in diesel engines? what am I missing?
While I was browsing the web, I came across something that makes me wonder. the auto ingnition tempreture of gasoline is higher than diesel, then why is compression ratio in a gasoline engine less than in diesel engines? what am I missing?





RE: Auto ignition
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Auto ignition
Petrol engine relies on a spark for ignition and has pre-mixed air and fuel. "Pre-ignition" - auto-ignition prior to the end of the compression stroke - is extremely destructive because the air and fuel are already mixed and ready to go bang, and must therefore be avoided, so the temperature at the end of the compression stroke must be BELOW the auto-ignition temperature by a wide enough margin to ensure that it does NOT occur.
RE: Auto ignition
Gasoline Combustion is a pretty complicated multi-stage process involving radical formation and other wild things in the "end gas" in the far reaches of the combustion chamber. The common explanation that high octane gas "burns slower" can be useful to understand the basics of detonation, but doesn't really reflect reality.
I believe this guy.
http://www.factorypipe.com/t_deto.php
RE: Auto ignition
An interesting example you might look at is a dual-fuel engine. It uses a compression ratio similar to CI diesel, a pre-mixed intake charge of air/NG, and a direct injection of a tiny quantity of diesel fuel to initiate combustion.
RE: Auto ignition
RE: Auto ignition
A spark ignited engine (gasoline engine) Does not want auto-ignition.
Bill
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"Why not the best?"
Jimmy Carter
RE: Auto ignition
Technically, neither a conventional CIDI diesel or SI Otto cycle engine wants auto-ignition (detonation) to occur. Both engines want a combustion process controlled by precisely timed injection or ignition events. There is no way to consistently and accurately control the auto-ignition/detonation process in a combustion engine.
RE: Auto ignition
I was under the impression that precisely timed fuel injection started the auto ignition process in a diesel engine.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Auto ignition
Auto ignition is by definition a largely uncontrolled process. A CIDI diesel uses precisely timed and regulated fuel injection to control the combustion process, so I would not consider it to be auto ignition. A modern high-pressure, high-frequency CR digital piezo fuel injector might use a half-dozen discreet injections per cycle, with pre-injections, main injections, and post-injections. The pre-injections reduce combustion noise, improve mixing of the main injection sprays, and reduce ignition delay. The post-injections help with exhaust emissions.
RE: Auto ignition
The former is a key property of every fuel. Every IC engine must somehow elevate the fuel beyond this temperature for combustion to occur.
The latter is an undesirable phenomenon where a portion of air-fuel mix gets hot enough to ignite at some undesired moment.
je suis charlie
RE: Auto ignition
RE: Auto ignition
RE: Auto ignition
RE: Auto ignition
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Auto ignition