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Just seen this on BBC news:
http://www.bbc.co.uk/news/business-40873093
Mazda is set to sell cars with compression ignition petrol engines from 2019, claiming they are 'up to' 30% more efficient than conventional petrol engines.
But, it begs the question why? Why is petrol compression ignition more efficient than spark ignition? I'm no engineer so ask the question for education, not to be cynical.
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
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Does not have a normal camshaft but each valve is moved up and down via it's own actuator. Sound more like a diesel than a diesel apparently
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
Remember, it's easier to criticise than create!
My guess, and I'm no expert, would be that because under compression it heats up uniformly, it ignites more efficiently than using a spark which is clearly at a single point in the cylinder and the ignition has to spread across the cylinder.
Also possibly the shape of the internal part of the cylinder, with no intrusion from a spark plug, would help.
Again, not attempting cynicism, just after clarity.
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
Whereas a spark ignites at a single point which has to propagate, so may be less efficient.
Even if I am right, it's probably a gross simplification!
Im normally very mechanically minded and I have a very good understanding of IC engines but the fuel efficiency gains from new tech is something that baffles me quite a bit.
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
I think.
How do they overcome detonation? I always thought that was the biggest issue in high compression petrol engines? The fuel tries to detonate at the wrong point in the cycle and bits of engine get spat out in pieces.
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
Detonation is bad in a spark ignition system as it creates forces that the crank is not designed to take. Diesels have different crank shapes for this reason.
A KH125 is a disc valve 2 stroke, that kind of engine is probably more prone to do that than a regular 2 stroke
High performance engines that have this issue usually use high octane fuel which is less prone or they start bolting water injection systems on to keep temps down.
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
Pre-ignition is what it sounds like, ignition before the spark caused by heat and pressure or to little advance on the spark.
Pre ignition destroys cranks. Detonation destroys pistons and rings.
High octane fuel does help by making the mix less prone to ignition from heat.
So I was wrong about them creating detonation
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
It seems to be saying that it will use normal spark ignition when under "high load", and compression ignition when under "lower load". I'm assuming "high load" is acceleration, and "lower load" is cruising or on the over-run. They seem to think this will improve fuel economy because they will use a much leaner mixture under the lower load conditions.
Or I might be completely misunderstanding it, I'm no engineer...
There is no 'H' in Aych, you know that don't you? ~ Wife
Turns out there is an H in Haych! ~ Sporky
Bit of trading feedback here.
Or is it just that they don't care much about money?
(obviously, I'm not counting all the companies doing EVs)