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I was looking at the EPA "Green Vehicle Guide" http://www.epa.gov/greenvehicles/Index.do and comparing my FEH to the non-hybrid Escape (AWD, 4cyl). The FEH emits 0.99 lbs/yr of "smog-forming pollution" compared to 5.3 lbs/yr for the non-hybrid Escape.
My guess is that the hybrid is cleaner only because the ICE shuts off at idle. I would think that both hybrid and non-hybrid would emit the same quantities of pollution once underway and moving at the same speed. Is this true, or am I missing something about the hybrid, maybe superior engine management or emission controls?
The Atkinsonized smaller engine means that even at idle, the FEH is a cleaner burning vehicle even if both engines are idling. Furthermore, the electric motor provides propulsion at all stages of propulsion (hence the hybrid term), which reduces demand on the ICE, an ICE with low power demand also is more fuel efficient then a vehicle under high demand, which a standard Escape experiences when they accelerate. Add in that the ICE goes into a lean burn to "off" when the demand for power isn't there, even at highway speeds, and the FEH continues to get cleaner and cleaner then it's sibling. ICE off operations during slowing and stoppages is just one part of the tapestry on why the FEH is so much greener and cleaner then the conventional Escape.
For those keeping track, from June of '07 to June of '08, I emitted 3.4 tonnes of CO2 as my vehicular Carbon Footprint. The average conventional 2006 Escape owner, driving the same exact miles, would've emitted 9.2 tonnes.
It largely depends on how the engine is tuned as Rich noted.
As another example, motorcycles typically get 40mpg or higher, but often produce 40 times the smog forming pollutants of a car. The main reasons being a lack of catalytic converters and being tuned for power, not efficiency.
Ok, their is also the fact that since they make up less than 1% of the US traffic, the EPA hasn't bothered to put new regulations on them since the 70s.
While the Atkinson engine cycle, and general tuning may play a role in the FEH's emissions, one should consider this: The CA version of the Ford Fusion, with a non-atkinson 2.3L also produces just .99 lbs of smog forming pollutants. See http://www.epa.gov/greenvehicles/Det...hicle_ID=70894
The details are explained here: http://www.greencarcongress.com/2005...milan_are.html Looks like extra fuel evaporative controls, variations on EGR, a stainless exhaust manifold to help the cat warm up faster, and other bits of tech.
So, while the Escape Hybrid MAY have reduced emissions because of the Atkinson cycle, it MAY also share emissions equipment with it's SULEV brother in the Ford Fusion.
While the Atkinson engine cycle, and general tuning may play a role in the FEH's emissions, one should consider this: The CA version of the Ford Fusion, with a non-atkinson 2.3L also produces just .99 lbs of smog forming pollutants. See http://www.epa.gov/greenvehicles/Det...hicle_ID=70894
The details are explained here: http://www.greencarcongress.com/2005...milan_are.html Looks like extra fuel evaporative controls, variations on EGR, a stainless exhaust manifold to help the cat warm up faster, and other bits of tech.
So, while the Escape Hybrid MAY have reduced emissions because of the Atkinson cycle, it MAY also share emissions equipment with it's SULEV brother in the Ford Fusion.
-J
Actually, as is my understanding per the FEH experience, it's the other way around. All the bits that they developed for the FEH was also transfered to the Fusion, which saw many of the benefits save for the Atkinsonized ICE in terms of pure engine materials. The FEH, were it not a AT-PZEV for it's hybrid drivetrain as a standard vehicle would've gotten a SULEV rating. Remember, the Fusion was initially developed to be released as both a conventional gas and a hybrid at the same time (Well, a three month difference). It's just that the hybrid version didn't get released on time. So, when I mentioned the Atkinsonized ICE, I meant not just the timing and cylinders and all that in the engine, but also all those nifty other bits as well.
The new Focus also uses some of the same mechanics as well as the eco-tec engine, or so said one of the Ford people at NAIAS 2008.
Simply think of the hybrid system as having a SUPERCHARGER that increases the HP/torque output of the otherwise rather small and highly efficient engine, a SuperCharger that DOESN"T BURN FOSSIL FUEL and often runs of FREE FUEL, kinetic energy that would otherwise be lost via brake heating.
That SUPERCHARGING effect allows you to run "normally", cruising along at a relative constant speed, with an inordinantly small and highly efficient engine.
The Atkinson Cycle has two distinct advantages. Because the intake valve remains open for the early portion of the compression cycle the compression pumping losses are quite significantly reduced. Look at the "push" torque available at the piston head in relation to the angular position of the crankshaft, it reaches its peak value when the "crank" position is 90 degree to the piston rod and is at its minimum both a BDC & TDC. If it doesn't have to do any "work" for the first ~30 degrees after leaving BDC....??
The second advantage is that the power cycle, fuel burn period, is effectively elongated. The explosive power of the fuel is more completely exhausted versus the standard "otto" engine.
Remember that "free", waste energy, the free, otherwise wasted energy that is used to run a turbocharger..?? Well, with an Atkinson or Miller cycle engine that fuel is no longer "wasted". Which is why you will NEVER see a turbocharged Atkinson cycle engine.
And as many RDX owners are currently discovering there are other shortcomings of turbocharging an engine.
Remember that "free", waste energy, the free, otherwise wasted energy that is used to run a turbocharger..?? Well, with an Atkinson or Miller cycle engine that fuel is no longer "wasted". Which is why you will NEVER see a turbocharged Atkinson cycle engine.
And as many RDX owners are currently discovering there are other shortcomings of turbocharging an engine.
But that's another story.
A turbo is driven off of the exhaust gasses, so you are saying that the Atkinson cycle doesn't put out exhaust gasses, or that they are so low pressure that they could not push a turbo?
I think Willard is kind of right. An Atkinson/Miller cycle engine does have enough exhaust pressure to run a turbo but this wouldn't work out very well. A turbo is more effective at high rpm. This is bad for economy for several reasons, mainly because the power losses inside the engine are so much higher. Superchargers (Miller cycle) are much more effective at low engine speeds where the Atkinson/Miller cycle needs help.
Low speed diesels do use turbos but they are optimized toward constant speed operation.
The low dynamic compression ratio of the FEH ICE results in significantly lower combustion temps, which minimizes the formation of nitric oxide. Oxides of nitrogen are major contributors to ground level smog formation, as CA found out when the lean calibrated CA cars of the 60's actually increased smog.
Why are Hybrids Cleaner?
