Why are Hybrids Cleaner?
 

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?

Re: Why are Hybrids Cleaner?
 

You're incorrect.

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.

Re: Why are Hybrids Cleaner?
 

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.

Re: Why are Hybrids Cleaner?
 

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

Re: Why are Hybrids Cleaner?
 

Oh man, I was going to say because we go thru a carwash on a weekly basis! ;)

Re: Why are Hybrids Cleaner?
 

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.

Re: Why are Hybrids Cleaner?
 

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.

But that's another story.

Re: Why are Hybrids Cleaner?
 

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?

Re: Why are Hybrids Cleaner?
 

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.

Re: Why are Hybrids Cleaner?
 

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.

Re: Why are Hybrids Cleaner?
 

The primary advantage of an Atkinson cycle engine is that MORE of the A/F mixture is burned during the power stroke, INSIDE THE CYLINDER, resulting in LESS heat/energy entering the exhaust system when compared to an "otto" engine.

Re: Why are Hybrids Cleaner?
 

My understanding is that combustion is essentially complete in the combustion chamber of any modern ICE. Exhaust flow/pressure is just dependent on the volume of air/gases exhausted from the engine which, although probably less in an Atkinson cycle, are certainly enough to make the exhaust flow out of the system and spin a turbo. As I said, not as effectively as a conventional engine but it would run. The most significant advantage of the Atkinson cycle is the asymmetry of the cycle where less energy is required in the compression stroke, providing more usable power during the power stroke since less is used during compression. Other than this effect, the Atkinson cycle would not be much more efficient than modern lean burn engines.

Re: Why are Hybrids Cleaner?
 

Just did a quick Google. Suburu has built a prototype hybrid with an Atkinson/Miller cycle turbocharged engine:

http://www.greencarcongress.com/2006..._introduc.html

Re: Why are Hybrids Cleaner?
 

Be that as it may, we all know that the bane of a turbocharged engine is the fact that you can't spin the turbine and produce BOOST unless a significant level of the product of combustion reaches the exhaust "stack". In an Atkinson cycle engine more of the "product" of combustion is used to push the piston downward, as opposed to the "otto" engine.

I'm somewhat surprised, obviously, to see the Subaru announcement. But the use of the electrics to take up the "slack" in HP/torque until the turbocharger begins producing boost is undoubtedly a good idea. It will be interesting to see how they overcome several of the other problems concerned with converting the Atkinson cycle technique into the Miller cycle using a turbocharged engine.

With the RDX, Acura has just learned, is learning, a hard lesson, if you're going to use a turbocharger to provide boost LATE in the "cycle" then you must derate the engine (low "native" compression) during normal "off-boost" running. Since the latter is the clear majority of the time, absent being on a race track, the FE suffers mightily.

The second issue with turbocharging a hybrid is the problem of keeping the catalyst heated to the operational level. But it looks as if Subaru is planning for their ICE to run continuously so that might not be a problem for them.

I guess we'll alll...

Stay tuned.

Re: Why are Hybrids Cleaner?
 

,,, and, because of the power assist availablity of the hybrid to help with small changes in power demand, the hybrid tends to deliver power within a narrower RPM range over the same road -- and that RPM range is in the optimum efficiency range for the engine.

Re: Why are Hybrids Cleaner?
 

I think the advantage you credit to the hybrid power assist should be more correctly attributed to the CVT. The CVT, unquestionably, allows the ICE to operate the clear majority of the time (no acceleration component) just barely above the point of knock/ping due to engine lugging.

There are two optimum efficiency range "bands" for the ICE, the lower RPM "band" resulting in the lowest possible frictional component but with relatively HUGE pumping losses, and the higher power output "band" where the opposite becomes true, pumping losses are minimized and frictional components go through the roof.

I personally think the power assist capability is best described as a form of supercharging, a HIGHLY efficient form of supercharging, allowing the use of a relatively small and therefore highly efficient ICE. ANYTIME the power requirement is above that of the smallish but HIGHLY efficient ICE the hybrid power assist will take up the "slack".

Excluding, of course, those times the ICE is not running at all.

Re: Why are Hybrids Cleaner?
 

I don't think supercharger is right; a supercharger uses a mechanical linkage that functions exactly the same at all RPM (increasing/decreasing with speed). The eCVT battery is much less predictable.

Re: Why are Hybrids Cleaner?
 

No, I was referring specifically to the more minor efficiency wherein the ECU does not change the ICE drive ratio becasue it simply does not need to, like a small hump or minor grade change that is temporary. It can handle the small difference in torque demand by simply using the power assist, so there is no need to change the engine speed. This, the ICE operates in a near constant RPM range, and is more efficient as a result.

If you drive an HSD hybrid, you have seen the assist come on for brief periods while in cruise and then go right back off. This serves two purposes: 1> It provides an opportunity for the ECU to use some of the stored energy if the battery is in a high SOC (so that any future regen energy has somewhere to go); and 2> it permits the ECU to manipulate the electric assist to maintain a near-constant ICE RPM (an ECU objective becasue its more efficient that way).

Conversely, when on a very slight downgrade (not enough for coasting), placing the MG system in regen has the effect of decreasing the (negative) torque demand on the ICE (a reduction in torque demand). If the MG load (either as motor or generator) is managed to as to handle the slightly decreased axle torque on the downgrade, no ICE RPM change is necessary. Once again it is more efficient realtive to whatever power it is producing.

This does not hold true for extended or steeper grades or coasting situations. There the CVT is the primary factor.

A hybrid is more that a CVT and an hybrid-adapted engine. It contains lots of little efficiencies that when combined make a big difference.

:angel: In this case, the Angel is in the details.

Re: Why are Hybrids Cleaner?
 

The main benefit of the "Atkinson"-cycle ICE, as I see it, is that by making the expansion stroke longer than the effective compression stroke, a higher percentage of the heat energy of the burned gases is being extracted during the power stroke than is the case in a standard Otto-cycle ICE. The engine is thus more thermodynamically efficient. The exhaust gases are consequently cooler (less wasted heat energy) than they would have been in a conventional ICE. But, the effective compression ratio of the fuel-air mixture (and so the work done compressing it) is still ~10:1 in an Atkinson-cycle ICE, just like a conventional ICE running on regular gasoline — it's the expansion ratio that is much larger (~13:1).

Stan