Engine Basics: Detonation and Pre-Ignition

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Engine Basics: Detonation and Pre-Ignition

Innleggfrá Ozeki » 15 Maí 2009, 14:38

Ég keypti mér mæli sem notar wide band O2 skynjara í púst til að sýna AF (Air/Fuel) hlutfall.
Er sem sé að tjúna til blönduna á krúsernum mínum. Á spjallboði fyrir svona almenn tjún-mál fann ég þessa áhugaverðu grein:

Engine Basics: Detonation and Pre-Ignition

Þarna er kveikjubank og fleira útskýrt, einnig falla fróðleikskorn um NorthStar og Chrysler Hemi vélarnar.


There are a lot of reasons forfast burn chambers but one nice thing about them is that they become more resistant to detonation. A real world example is the Northstar engine from 1999 to 2000. The 1999 engine was a 10.3:1 compression ratio. It was a premium fuel engine. For the 2000 model year, we revised the combustion chamber, achieved faster bum. We designed it to operate on regular fuel and we only had to lower the compression ratio .3 to only 10:1 to make it work. Normally, on a given engine (if you didn't change the combustion chamber design) to go from premium to regular fuel, it will typically drop one point in compression ratio: With our example, you would expect a Northstar engine at 10.3:1 compression ratio, dropped down to 9.3:1 in order to work on regular. Because of the faster burn chamber, we only had to drop to 10:1. The 10:1 compression ratio still has very high compression with attendant high mechanical efficiency and yet we can operate it at optimum spark advance on regular fuel. That is one example of spark advance in terms of technology. A lot of that was achieved through computational fluid dynamics analysis of the combustion chamber to improve the swirl and tumble and the mixture motion in the chamber to enhance the bum rate.


Hemi racing engines would typically knock the ring land off, get blow by, torch the piston and fall apart. No one then understood why. We now know that the Hemi design is at the worst end of the spectrum for a combustion chamber. A nice compact chamber is best; that's why the four valve pent roof style chambers are so popular. The flatter the chamber, the smaller the closed volume of the chamber, the less dome you need in the piston. We can get inherently high compression ratios with a flat top piston with a very nice bum pattern right in the combustion chamber, with very short distances, with very good mixture motion - a very efficient chamber.
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Buick '73

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