An Ob-NOx-ious truth

In a recent post I extolled the benefits of running even a large vehicle on biodiesel. I focused mostly on the CO2 emissions, since that is the big buzz word, and the commonly known greenhouse gas.

I failed to discuss other emissions from such an engine and fuel combination. I'd like to talk about that now.

First, the good news. For all emissions excepting NOx, biodiesel burns cleaner than petroleum diesel, and in many cases cleaner than gasoline. You can see exactly how much so in this summary from the biodiesel board, which uses the EPA's own research as it's source.

Now, the bad news. Burning biodiesel does not help mitigate it's high NOx emissions. Actually, the research has yet to prove if biodiesel noticeably changes NOx emissions either for better or for worse as compared to petroleum diesel. However, the fact remains that NOx emissions for a diesel engine is drastically higher than that of a similar output gasoline engine.

Why? Well, I'm not a scientist, and I can't present my own measurements and findings, but I can tell you is that my research has told me that NOx is more-or-less a byproduct of heat, and compression in the context of an internal combustion engine. Unfortunately, I can't find any single resource to link you to that summarizes it elegantly and succinctly (except maybe this), so you'll have to take me at my word, or do the research yourself.

With that said, it becomes readily apparent why diesel engines, regardless of the fuel they are consuming, would have a higher NOx emission. A diesel engine depends upon heat and compression to ignite the fuel, so it is by nature going to have higher NOx emissions. Using biodiesel should not significantly change this, since it's still being ignited in the same way.

Now, not all is lost the Tier 2 Emissions standard that the EPA is imposing in 2009 addresses NOx emissions, and NOx is in-fact one of the primary reasons for the new standard. In order to meet these standards manufacturers are using all sorts of different strategies. Some of them are new and innovative like urea injection and "self cleaning" particulate filters. Others have been around for years in gasoline vehicles, like exhaust gas recirculation (EGR) and Catalytic Converters. While these new emissions standards and equipment do pose a bit of a challenge for those manufacturing performance and aftermarket equipment for these vehicles, overall I think it's a step in the right direction. Besides, many companies already have performance tuners and exhaust systems for the 6.7L Cummins diesel, and the 6.4L Ford Power Stroke, both of which meet the stringent new Tier 2 emissions standards.

I see your Prius, and raise you an Excursion.

So, for probably the past 8 or 9 years, I've been infatuated with diesel engines. Ever since I was introduced to an early 90's Dodge Ram 2500 with the 12 valve Cummins motor. I was impressed with the sound of the motor, the apparent torrent of torque and horsepower, and the remarkable fuel economy considering it's size.

Ever since, I've lusted after vehicles with diesel engines. However, I'm also a bit of a "gear head" and have a bit of an addiction to performance, particularly the kind associated with small, light vehicles with a reasonable amount of horsepower, and excellent handling. I've also never really had a "need" for one of the vehicles that usually have optional diesel motors as they are usually very large and meant to do serious industrial type work.

So what does all of this have to do with a Prius? Well, for nearly as long as I've been interested in diesel I've had a desire to own a Ford Excursion with a diesel power plant. If you're one of the increasing number of people who are trying to live "green" you're probably clutching your chest and gasping. If so, consider this.

A Toyota Prius is considered to be the ultimate "green" automotive conveyance. So let's use that as our baseline.

2007 Toyota Prius
MPG 60(city)/51(hwy) -- Assume 55.5 as average fuel economy 60+51/2=55.5
10,000 Miles Per year
10000/55.5=180 gallons of gasoline
180*19.4=3492 lbs of CO2 emitted into the atmosphere annually

2005 Ford Excursion (Diesel)
MPG 15(city)/18(hwy) -- Assume 16.5 as average fuel economy 15+18/2=16.5
10,000 Miles Per Year
10000/16.5=606 gallons of diesel
606*22.2=13453 lbs of CO2 emitted into the atmosphere annually

If you're curious my MPG numbers for the Prius comes from its EPA rating, and my MPG numbers for the Excursion come from estimates based on average mileage people have reported on various forums, so there is a little room for interpretation there. My CO2 emissions per gallon of fuel is based off the EPA's own findings.

So, already there is an obvious difference, the Prius dumps almost 10,000 fewer pounds of CO2 into the atmosphere than the Excursion. Take that earth destroying consumerist, you say? What if that same Excursion were fueled by 100% biodiesel?

According to The National Biodiesel Board, biodiesel emits 78% less CO2 than petroleum diesel. That changes our equation considerably.

22.2*.22=4.884 lbs of CO2 per gallon of biodiesel.
606*4.884=2959.704 lbs of CO2 annually for the same Excursion driven 10,000 miles a year on biodiesel!

That's over 500 FEWER lbs of CO2 than the Prius! Now I can already hear you saying.. But the Excursion has to burn over 3 times as much fuel as the Prius, what about refining and transporting all that fuel? True, that will increase the Excursion's carbon footprint again, probably to a point where the Prius is again the "greener" option. But, consider this.

Say you put together a small biodiesel refinery. Now, say you mounted said refinery to a suitable trailer chassis. Now, say that you put a couple solar panels, batteries, and pumping/heating equipment on the trailer as well. Why, all of a sudden, you have a mobile biodiesel refinery that is self sustained, and can be pulled by the aforementioned Excursion to your local fast-food joint to pick up oil. I suspect a system like this would cost less than $5,000 and would easily supply one or two diesel powered vehicles in a household. That should mitigate the carbon footprint of getting the fuel!

Also, consider that biodiesel is "carbon neutral", meaning that the only carbon it emits is carbon that was absorbed by the plants from which it is made. Good stuff.

Starts to look pretty compelling vs the Prius which likely won't last the 300-600k miles a diesel motor would. Nor could a Prius haul 8 people, luggage, and a trailer someplace.

Now, I'm not saying that it's the perfect choice for everyone, but it should make the point that blindly accepting that any one "green" solution is the silver bullet is foolish. I also hope I helped to demonstrate that not all things are as they appear. So next time you see a diesel powered large truck, consider that it may not be "killing the planet" but might be coming awful close to the emissions of a vehicle designed to be "green". That is, if it's running biodiesel.