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Infiniti rolls out industry-first variable compression engine


jasonj80

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I think I read an article awhile back. But it was labeled at the time as a Nissan engine.

 

Kudo's for engineering ability. But I guess I just don't see the point. Doesn't turbo essentially give you variable compression? Higher boost equals higher compression. Low boost is low compression.

 

I guess I'd rather see Ford go the HCCI route with compression detonation than this.

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I think I read an article awhile back. But it was labeled at the time as a Nissan engine.

 

Kudo's for engineering ability. But I guess I just don't see the point. Doesn't turbo essentially give you variable compression? Higher boost equals higher compression. Low boost is low compression.

 

I guess I'd rather see Ford go the HCCI route with compression detonation than this.

 

Forced induction is closer to variable displacement than variable compression. If you force twice as much air in (14 PSI on the turbo at sea level), then you essentially double the displacement of the engine.

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Doesn't turbo essentially give you variable compression? Higher boost equals higher compression. Low boost is low compression.

 

Most turbocharged and supercharged spark ignition and diesel engines in production cars and trucks have a constant compression ratio. This is the difference between volume in the combustion chamber when the piston is at BDC and when the piston is at TDC. The turbocharger doesn't change this ratio. For example, on the JLR Ingenium 2.0L turbo diesel the difference between BDC and TDC is always 15.5:1.

 

The original Miller Cycle patent in the 1950s was effectively a variable compression ratio design. Modern engines that use Miller Cycle like Nissan HR12DDR have a constant compression ratio but a larger expansion ratio by holding the intake valve open longer compared to Otto Cycle. http://www.nissan-global.com/EN/TECHNOLOGY/OVERVIEW/hr12ddr.html

 

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For a "recent" smaller application of the Miller cycle, take a look at one of the V6 engines that was offered in the Mazda Millenia S. The problem with "Spit-Back" is that it does make meeting environmental emissions a bit more difficult vs. the normal Otto cycle. The Nissan approach here attempts to get all of the benefit and as little of the problems as possible. It does, however, add to engine complexity.

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