On-Board Distillation System for Reduced HC Emissions and Improved Fuel Economy
31 August 2006
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| Layout of the On Board Distillation System. Click to enlarge. |
Researchers at the University of Texas have developed an on-board device that dramatically reduces start-up emissions of unburned hydrocarbons.
The on-board distillation system (OBDS) extracts high-volatility components from gasoline and stores them for exclusive during start-up and warming. New tests show that OBDS reduced cranking fuel requirements by 70%, enabled a 57% decrease in catalyst light-off time, cut the emissions of regulated hydrocarbons (NMOG) by 81%, and delivered an apparent 1% increase in fuel economy. The team reports on its work in a paper in Environmental Science & Technology.
In modern vehicles, 60-95% of all HC emissions occur during the first 90 seconds after a cold start.
The primary reasons for this are twofold: low/unknown fuel volatility and poor catalytic converter efficiency. The relatively low volatility of gasoline (10-30% vaporizes upon injection at 20° C) requires the injection of considerably more fuel (typically 8-15 times) than the stoichiometric amount in order to generate a reliably ignitable fuel/air mixture.
Furthermore, the volatility of the fuel is not known a priori by the engine controller (the powertrain control module, PCM), so the PCM is often calibrated to command fueling rates based upon the expectation of the worst-case volatility fuel. This results in an air/fuel mixture that is overly fuel-rich for most starting conditions and a large amount of liquid fuel that will enter the combustion chamber during the first several cycles. Much of the excess fuel exits the engine unburned or only partially combusted.
A conventional three-way catalytic converter will not reach “light-off” temperature (corresponding to 50% HC conversion efficiency) for 30-40 s or more during the FTP drive cycle. Ironically, the period of highest engine-out HC emissions coincides with the period of lowest catalyst efficiency, making the combination of low fuel volatility with poor catalysis the primary cause of high HC emissions during the cold-start and warm-up period.
(This is also a design consideration for plug-in hybrids, as the longer periods of all-electric drive could be accompanied by more engine cold-start events during the day.)
The OBDS originally was designed to address the cold-start problems inherent in E85-fueled vehicles. The OBDS separated the most volatile fractions of gasoline from E85 for use as a starting fuel. The Texas team of Marcus Ashford and Ronald Matthews then developed a version of the OBDS specifically for gasoline vehicles.
The OBDS intercepts fuel from the main tank. Startup-fuel is extracted by distillation and stored in a separate “light ends” tank for subsequent use; the heaver gasoline fraction is routed back to the main fuel tank. Engine coolant provides the heat source for the distillation process; thus, the start-up distillate is best made when the engine is hot.
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| Comparing Emissions Indices. The OBDS Navigator has a lower EI (NMOG) than the two ULEV vehicles and is only slightly higher than that of the PZEV Sentra. Click to enlarge. |
The researchers installed this OBDS on a 2001 Lincoln Navigator equipped with a 5.4-liter 32-valve V-8 engine originally calibrated to meet federal Tier I emissions standards.
With the use of the OBDS, the emissions index for the Navigator was lower than a MY 2000 ULEV Honda Accord and Toyota Camry, and only slightly higher than that of a MY2003 PZEV Nissan Sentra. The emissions index (EI) is a measure of the emissions produced with respect to the fuel consumed in the process. The emissions index effectively normalizes mass emissions by engine displacement and vehicle mass, two factors that tend to negatively impact traditional mass/distance emissions measurements.
The research suggests that a smaller vehicle equipped with OBDS may be able to meet SULEV/PZEV tailpipe hydrocarbon requirements “without having to resort to semi-exotic catalyst and engine control strategies.”
The researchers estimate that the system would add about five pounds to a car’s weight and less than $100 to its cost when in full production. The research was funded by Ford Motor Company, the US Department of Energy, and the Texas Advanced Technology Program.
(A hat-tip to Martin!)
Resources:
“On-Board Generation of a Highly Volatile Starting Fuel to Reduce Automobile Cold-Start Emissions”; Marcus D. Ashford and Ronald D. Matthews; Environ. Sci. Technol., ASAP Article 10.1021/es051950t S0013-936X(05)01950-4
Nice, but is there not a similar system already on the market? Another thing is with E-x gasoline in this system, the ethanol may become the predominant fraction in the Light Ends Tank. How will this work with butanol? I assume that this may also be done with diesel. However, biodiesel, and xTL liquids that are chemically homogeneous, may not benefit. Perhaps a fuel heater (via engine coolant, electric elements, or vacuum flask stored heat) would help with fuel vaporization.
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___Another method to control emssions would be to delay, stagger, and gradually turn on cooling systems. That way, the engine, motor oil,and exhaust heats up quicker, and so will the catalytic converter. With the engine and catalytic converter warmed up faster, the emissions are lower. Fuel spent during this period will also be lower.
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___As to vacuum flasks, the Prius uses it to shorten engine warmup and reduce idling and emissions.
Posted by: allen Z | 31 August 2006 at 11:08 AM
Read the article allen Z, it states, "The OBDS separated the most volatile fractions of GASOLINE [emphasis added] from E85 for use as a starting fuel." Yes it was tested WITH E85 and it separates the GASOLINE volatile components.
Electric water pumps and thermostats to elicit strict control over the cooling system are still waiting for the industry to turn to 42V systems.
Posted by: Patrick | 31 August 2006 at 11:15 AM
Coolant has to circulate the block or else it will warm up overly hot in some areas while still being cool in others. This can cause oil coking and causes the block and/or head to warp and can lead to very, very fast failure, especially in the case of cylinder heads warping and causing the head to lift enough to blow out the cylinder head gasket or permit oil and coolant to intermix.
With the thermostat closed (which is a mechanical device, no need for 42v), there is no cooling going on, the coolant only circulates to maintain uniform warming of the entire engine block and cylinder head(s). The only way to accellerate this process would be like the system reportedly on the Prius II where it has a thermos for the coolant to circulate hot coolant after each startup.
Posted by: Sid Hoffman | 31 August 2006 at 01:31 PM
The thermostat is a mechanical device which undergoes hystersis as it approaches the operating temperature it is still letting coolant pass. It does not just open and close instantly and this effects efficiency. An electrical thermostat would improve warm up times and would not require a 42V system. An electric water pump would require a 42V system but would improve the efficiency (less driveline loss, circulating coolant at the rate needed and not just increasing the flow due to rpm).
Posted by: Patrick | 31 August 2006 at 01:56 PM
Fascinating idea, but when we start looking at onboard fuel distillation equipment, it's hard to see that as a "simpler" approach to emissions. Maybe it will work well, or maybe it will be the EGR valve of the 2010's. How do we know that the heavier portion of the gasoline or E-fuel won't cause problems with combustion or fuel system clogging with the ligher portions removed from it? Anyway, why not just carry around a small tank of butane or some other volatile fuel to use for the cold start and progessively use less of for the first 90 seconds or so until you're running on just gasoline or E-x mixture?
Posted by: zach | 31 August 2006 at 02:05 PM
zach, you cannot require (by law) an owner of a vehicle to do any maintenance on an emissions system (such as refilling a butane canister) earlier than 100,000 miles. This is why they have 100,000 mile warranties on emissions related components and where BMW is going to battle with the EPA over ADBlue right now.
Posted by: Patrick | 31 August 2006 at 02:09 PM
The new Mini will have an on-demand water pump, driven by a friction wheel. There was an article about it on this site two weeks ago.
Posted by: Bernard | 31 August 2006 at 05:28 PM
Patrick - that sounds like the current state of the law, but why not change it? In this case it seems like there would be a much simpler technological solution if the law was changed to allow manufacturers to design cars that will only start with butane in the butane tank (or whatever fuel worked best).
Posted by: Zach | 31 August 2006 at 07:47 PM
I think this is simple enough technology and I hope it is used. It is better than storing the exhaust for processing later as SAAB did, and could even be combined with that system as there would be less exhaust volume. I have considered that just heating the fuel in the fuel rail/injectors might help quite a bit.
As for water pump control, why not a magnetic clutch as used on an A/C compressor?
Posted by: John Schreiber | 01 September 2006 at 12:20 AM
12Volt electric water pumps are common DIY replacement items available for common muscle car V8 engines. There is no need to wait for 42volt systems.
Posted by: Rich | 01 September 2006 at 05:10 AM
Note also that that Law you just wanted to get rid of is the same one that mandates that you have a 80,000 to 100,000 mi waranty on hybrid batteries.
This whole onboard distillary is not all that different from what you have now, cars already have a charcoal canister to catch gasoline vapors and burn them off later, I see no reason why the current evaporative emmisssion components could not be modified to work in a similar manner to reduce cold start emissions on gasoline vehicles.
In brazil the cars have a 2nd tank for gasoline to ease starting on high ethanol blends.
Posted by: rj | 01 September 2006 at 07:37 AM
Rich, those 12V pumps just run full blast and I believe you ordinarily remove the thermostat in order to use them. The cars which typically use those 12V water pumps are often drag cars stripped of most electronic goodies and they don't cruise down the highway all day long getting stuck in traffic on a hot sunny day.
http://www.superchevy.com/technical/engines_drivetrain/accessories_electronics/0408sc_pump/
Typical 12V water pump gives you about 35gallons per min. for a V-8 application.
Typical mechanical water pump gives you about 25gallons per minute at idle and up to 90 gallons per minute at 5000rpm.
You won't get close to 90gpm with a 12V pump that fits in the space available.
Posted by: Patrick | 01 September 2006 at 08:41 AM
As an engine leader BMW has not waited, the lastest 3 series has the electric water pump.
http://www.edmunds.com/insideline/do/Features/articleId=115127
Good stuff.
Posted by: Bill Walsh | 04 September 2006 at 09:39 AM
First off, University of Texas-El Paso demonstrated this in the Future Truck competition a few years ago (2000, IIRC). It's nice that they only needed six years to get the blasted thing patented. The deal was that they needed to get an E85 vehicle to start well in cold conditions (difficult with E85) and keep clean emissions during starting - warmup. They distilled the lighter, petroleum-based fractions from the E85 (using waste heat from the engine), stored that in a separate tank, and used that for starting, switching over to regular E85 fuel once the engine warmed up. The result was that it started easily and warmed-up cleanly.
It seems it only took six years or so from first demonstrations to patenting. I wonder how many more years it will take to get it into production vehicles. I also wonder just how difficult it would be for another company to independently engineer something similar (and find a way to bypass Ford's very-slow-moving patent) and beat them to the market with it.
Posted by: DaChesserCat | 05 September 2006 at 11:29 AM
Correct me if I'm mistaked, but hasn't been about a decade now since we've been hearing about the switch-over to 42 volts?
Posted by: Dursun | 06 September 2006 at 03:52 PM
Yes, it was brought up in the early 90s and some suppliers were getting ready by the late 90s for an introduction around 2004-2006. They decided it would be too costly for all the suppliers and scrapped their plans as they developed more powerful 12V alternators (increasing efficiency slightly and employing water cooling and other efforts). It was far easier to change the US from 6V to 12V since now we have 100 times as many cars on the road.
I'm hoping for hybrid technology to push 42V development along. It sure would make micro-hybrids easier to institute (getting the 3-4 kW of power out of a 42V system is easier than getting that kind of power out of a 14V system and you need atleast that much power to give the slight assist for initial launch and quick silent start up of large motors).
Posted by: Patrick | 08 September 2006 at 11:11 AM
Watever happened to the "On Board thermocatalytic fuel cracking" systems that could get up to 85 mpgs... the ones that started with the 'Pogue' carburettor in early 1920s... are these 'on board distillation' systems the only meagre result ? Thks for any update ...
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