Two in one day. Beauty. This is why I want the EPA and CARB to relax NOx emission rules so we can get more diesel cars on the road. With a larger market for biodiesel on the road, making the switchover to algal oils will be smoother.

There are two viable solutions that I know of that can make diesel vehicles meet existing and future 50-state NOx rules. The urea-based catalytic systems from Daimler and the plasma-arc system that Honda will be using. Both seem to be near ready for production. Not sure which one will be more cost effective or less problematic. All things being equal, Honda's does not require any infrastructure to periodically dispose/replace the urea solution. In fairness, those intervals are quite far apart (I believe something like every 10k miles or more). For some reason, I'd bet on Honda's solution.....

Angelo -

you'd lose that bet. SCR systems are fully developed and operational in virtually all new trucks in Europe, because they have to meet the strict new Euro 4 regs. Mercedes has downsized the system and is looking to introduce it to the US market - so far, EPA and CARB are reluctant to approve it. Among other reasons, the infrastructure for distributing the AdBlue additive does not exist in the US. MB claims its system can make do with a refill once every 3000 miles.

Honda's plasma-arc system is at a much earlier stage of developement. Afaik, there has not yet been a convincing demonstration that it actually works - please let me know if you've seen a publication to the contrary.

SCR technology is well developed and working fine for many years in stationary diesels. Now it is fully adapted to heavy trucks and some cars. The problem is that SCR diesel fleet requires extensive urea replenishing infrastructure and it is virtually impossible to control if individual drivers replenish it or not. Those are the reasons US EPA is pressing home another technology – regenerative NOX absorbers. The only additional chemical injected is diesel fuel, injected to exhaust stream to burn excess oxygen and rise exhaust temperature in periodical events of absorber’s regeneration. Prognosed fuel consumption penalty varies widely in different sources, between 0.5-2%. Generally this additional amount of fuel costs way less (and carry less fossil fuel energy equivalent) then urea, but because of artificially overpriced transportation fuel in Europe urea injection appears to be cheaper.

JRod -

not sure what VW was trying to achieve by injecting diesel into the exhaust. The usual method for bringing the oxidation catalyst up to its light-off temperature quickly is to inject additional fuel into the cylinder during the expansion stroke. This is only done for about 30 secs after a cold engine start.

Paul, Andrey -

EPA and CARB are indeed worried about owners (e.g. commericial haulage operators) that might want to defeat the system. After all, the engine will run just fine without the aftertreatment. The additive raises the cost of consumables by about 2-3%. This was a concern for European regulators as well, which is why they insisted on supervision of both the additive tank level and the chemistry of its contents by sensors reporting to the OBD. If there is not enough additive, or it has been diluted/replaced by e.g. plain water or a sensor has been tampered with, engine operation is limited to an emergency mode.

EPA and especially, CARB, are quite a bit more paranoid about system defeats in general. They do not much like SCR because the notion of a consumable catalyst is new in the automotive sector. Also, just as certain European carmakers resisted the adoption of three-way catalyst technology that US companies held patents on back in the 80s, there may be an unspoken economic motive for the US stalling on SCR simply because those patents are in European hands. That's just my suspicion though, not an allegation I can back up with hard evidence.

Another reason is that the US test cycle yields lower exhaust temperatures than the European one. US regulators are holding out for more effective NOx store catalysts, because they have slightly higher *initial* conversion rates. Unfortunately, even the 15ppm in ULSD are enough to poison such a device fairly quickly. You need to sustain temperatures of 650 deg C in the monolith for ~30 minutes to reover to about 90% of initial conversion efficiency. B100 biodiesel and pure xTL synthetics do not contain any sulphur at all but cost a lot more and are not generally available.

In an LDV, NOx store catalysts and need to be mounted in the vehicle underbody in an LDV, therefore prolonged excursions to such high exhaust temperatures raise the long-term average fuel consumption by 2-3% initially and 5-10% later in life. The application overheads and life expectancy of NOx store catalysts are also still unacceptable, which is why VW, Audi, Mercedes and others have switched back from stratified (i.e. lean-burn) to stoichiometric homogenous gasoline direct injection.

EPA's aggressive Tier 2 program for NOx emissions from HDVs calls for 80% reduction by 2010. Industry experts believe that engine-internal measures such as high rates of cooled EGR or HCCI combustion in part load will not be sufficient to achieve the new levels and that NOx store catalysts will not achieve adequate life expectancy (750k miles) in this timeframe. By default, US bus and truck manufacturers may have little choice but to follow Europe's lead and adopt SCR after all. At that point, an AdBlue infrastructure will need to be established.

Allen -

biodiesel doesn't contain any sulphur to begin with, so no ethanol is neccessary to meet SOx regs.

Using a port fuel injection of ethanol might be possible even at high compression rates as long as the mixture is lean enough to avoid auto-ignition. The high evaporation heat of ethanol would cool the fresh charge, leading to lower NOx.

PM reduction depends primarily on the pressure at which the diesel is injected, and charge motion (swirl). If a combustible substance is already present in the charge, it will compete for the available oxygen with the diesel. Whether you end up with more or less PM depends on the specifics of the combustion process, including the ratio of the fuel masses.

Premixing ethanol and diesel is a major no-no because ethanol is hygroscopic and will preferentially dissolve in any water present. Therefore, unless you use a stabl emulsion, your fuels would separate in the tank. Another problem is that any ethanol fraction would be more likely to cause cavitation in the common rail injector nozzles.

Diesel injection is sometimes used in very large engines that are retroffitted for gaseous fuels, such as methane or hydrogen. In those cases, the very small diesel injection replaces the spark plug. Such systems are not normally used for on-road vehicles, though.

What about hydrogen injection?

http://thefraserdomain.typepad.com/energy/2005/11/hydrogen_boost_.html
http://www.hy-drive.com/main/Default.asp?Page=20
http://www.greencarcongress.com/2005/11/hydrogenenhance.html
http://www.wired.com/news/autotech/0,2554,69529,00.html

An Engineer -

intriguing idea, especially since farming algae there would not much interfere with an existing ecosystem - there is virtually none. The fresh water sheet on the surface means you could use algae that can tolarate brackish water but not true salt water - inherently limiting the potential for uncontrolled spread beyond the dead zone. A third advantage would be the nearby megarefineries, which could handle the transesterification step required to produce biodiesel.

One snag is that algae do need oxygen to grow, and there is only a little dissolved in the fresh water sheet. Natural diffusion of gases into liquids is a rather slow process.

Another snag is that the Gulf of Mexico is subject to fully formed hurricanes. Their impact on algae farms and algae accumulation on the beaches and inland due to storm surges would need to be considered. If it takes a long time for the farms to recover, you could end up with a fuel supply bottleneck.

Rafael,
You are wrong about algae needing oxygen. Note that all photosynthetic organisms, including algae, produce oxygen. In wastewater treatment systems, algae are sometimes used to introduce oxygen, which is then used to degrade organic pollutants.

As for the effect of huricanes, it would be no different from the existing situation - I am not sure what the hurricanes do to the dead zone.

I guess I should have pointed out that all you need is a way to harvest the dead zone. My proposal: a ship-based DAF system. The ship (or fleet of ships) would trawl the dead zone harvesting the algae, until it has a large load. The load of concentrated algal soup would then be unloaded to land-based processing facility.