Quote:
Originally Posted by Dave's Civic Duty
It was surprising to see the now 16 year old lean burn Civic produce less than either of Honda's currently best examples.
Totally. 
I don't understand why they weren't put in even more Honda's. & whey did Honda keep the VTEC-E such a secret? I've owned many Honda's over the years, I didn't learn about the lean burn until a few months ago. What an amazing design, especially for a production car. Can't this technology be further developed?
Dave |
I don't want to come off as a naysayer, or defender of regulations, but a lot of these issues are more complicated than they may seem at first glance. I also am not an expert in this particular area, so take the following with a grain of salt.
One big problem with this lean burn technology is that it only works at light loads. When you place demand on the engine, it is going to work pretty much like any other engine. When you are running in those ranges, you are going to pollute like any other engine. So, you probably want emissions systems.
The problem is that when you are burning lean, you have a cool, O2 rich exhaust which not only renders a cat ineffective, it rapidly destroys it. So you end up with an engine that puts out higher NOx at low loads, and which is waay dirtier at high loads.
Now, the natural question is, how could that be? Look at the comparison in total gasses! But that assumes that we are comparing apples to apples. Look at the vehicle weights and performance stats of the vehicles being compared.
Car makers gave consumers what they wanted. Bigger, faster cars, filled with Barca Lounge Chairs with built in cup holders.
As engines get bigger and bigger, low load operation moves farther and farther out of the engine's "efficiency island". Think about it, a big SUV needs a big engine to start hauling 8 people and a boat, but only 15-20 HP to maintain speed with 1-2 people on the freeway. So that big engine is throttled waaaay back. That is effectively vacuum, which drags down the VE of the engine. You can only expand compressed gas to the ambient pressure, so this is a very inefficient way to convert energy.
As Honda started making heavier cars, the lean burn engines had to get bigger, and they got dirtier, because they were operating less efficiently more of the time. To get the pollution down to permitted levels, they first looked at running leaner, but at stoichiometric ratio. That may sound like a contradiction, but 'leaner' doesn't have to O2, it can be exhaust gas. I'd have to go looking at some of the papers, but the general problem with this was that it only worked if you eliminated turbulence (I think it had something to do with thermal boundary layers). That is, you had to get rid of the vortex generation.
But the vortex generation is what was permitting the lean burn to be used efficiently! So it was a catch 22...
Really, the problem is three fold. First, there is a matter of consumer taste. If consumers would buy lighter, lower frills vehicles, we could make them more fuel efficient than the same vehicles where two decades ago. The second problem is political. Look at the comment about diesel above. The big barrier to those technologies in the US was not emissions regulation, but the money and politics behind sulfur heavy fuels. In many ways, regulation is at the wrong end of the problem, but money and politics make any other point of regulation very very hard. The last problem is control. There are some very promising paths to better efficiency, for example, we were just talking about HCCI here. But there needs to be some technological innovations to reliably deploy these techniques at the consumer level.
Hopefully, I am at least involved in #3 in a small way. One and two are beyond my control. I don't even check the box to donate a couple bucks to campaigns on my tax return, so it is safe to say that my political clout is zero...
-jjf