Don't feel to bad when I got my first 2 tanks of ULSD last year while on vacation I saw my mileage drop 2.5 mpg from 18 down to 15.5 mpg. Once I was 100% back on LSD my mileage went back up to where it was before. I've read some post where people said they got better mileage from ULSD. The only way I can get some of my lost mileage back is to use Lucas at every fill up and drive 55 MPH. Oh I now get all most the same fuel mileage (with fuel additive) driving 55 MPH burning ULSD that I use to get while driving 75 MPH burning LSD without fuel additives [:@]

 

Don't forget the OTHER sink in mileage once the winter mix hits. [:@]

 

How much of a loss in mileage do you see in the winter months?

 

I think I loose anywhere between 1-2 mpg in the winter.

 

MikeCTD,

ULSD doesn't necessarily have lower cetane than LSD. Cetane isn't the issue when discussing ULSD and LSD. Fuels have a rated amount of power that can be gotten from them for any given amount. It is measured in British Thermal Units (BTU's). For example, gasoline is rated at 114,132 BTU's per gallon. Diesel is rated at 138,000 BTU's, and for the sake of the discussion, since it was mentioned, ethanol alcohol is only 76,000 BTU's per gallon and methynol is even lower at 56,800 BTU's. The alcohols though have incredibly high octane ratings and are thus suitable for very high compression engines (hence their use in alcohol dragsters)...but as mentioned, the very low BTU value means you gotta burn huge amounts of it to make any power.It's easier to builda fuel system that will pump the necessary volume to make the power than to try and overcome the knock issues at high compression and lower octane.

So, as you can see, we get more energy from a gallon of diesel than gas. This is why a diesel engine will generally have a higher HP and/or better mileagerating when compared to any gasonline engine of the same displacement. I say generally because there are just so many factors involved and real world examples where this is not true, but it is true in general.

Another factor that comes into play are the additives put into the fuels. In the case of gasoline, additives are put in to increase octane. In the recent past the additive had been methyl tertiary butyl ether (MTBE, or sometimes just referred to as MTB for short).Prior to MTBE were the high aromatic unleaded fuels, and prior to that were the actual "leaded" fuels(for anyone old enough to remember that). MTBE is derived from methynol and is used as an oxygenate in the gas to increase octane and to promote more complete burning of hydrocarbons (emmissions reduction). Clinton and Gore enacted legislation in 2000 to eliminatethe use of MTBE because it is considered a carcinogen and will mix with water (fear of contaminated water supplies and ground water, etc). So, a suitable replacement had to be found. That replacement is ethanol. It increases the octane to suitable levels, and decreases some of the other emmissions that were considered problematic. It's not a panacea however, ethanol introduces other issues of its own, like absorption of water, lowering theenergy contentof the gas it is blended with, erosion of elastomeresand an increase in other emissions that aren't necessarily good either.

Either way, the point is, the BTU rating of pump gas varies depending on the additives in it. The BTU ratings I gave above are for the purest form of each (i.e. no additives of any kind). Each oilcompany blends it's own gas with additive packages derived by their chemists. Of course, they are restricted in what they can use and have specific limits onthe levels of content, etc. The additives are designed to do many things. Detergents to help clean the fuel system and reduce deposit build up in the engine. Aromatics to increaseoctane, as well as oxygenates to do the sameand reduce emissions (each with their own list of pros and cons). The use of the various aromatics, oxygenates, etc is constantly being researched to monitor emissions, etc. The formulas change as legislation is enacted to prevent or limit the various additives depending on recorded emission data and required/desired performance levels.

In the case of diesel, one of the components is sulfur. Sulfur adds lubricity to the fuel and isnecessary for the fuel system components. Lower the lubricity and parts start to fail or wear out. This was one of the arguments surrounding the replacement of LSD with ULSD. However additives are put into ULSD to boost lubricity back to LSD levels and to also replace the power lost in the process of making ULSD (the process strips certain levels of aromatics from the fuel, causing a drop in BTU value for the given quantity). The argument that ULSD will lower mileage (due to lower energy content) may or may not hold true and most likely will depend completely on the additive package each oil company puts into its pump diesel. Personally, I think we're gonna see some diesels that are "better" than others during this period of transition from LSD to ULSD (ULSD will be the only available diesel starting in 2010) and if posts here are any indication, we already are seeing this difference. Eventually, the oil companies will all have additive packages that are relatively the same and then we will see a stabilization in diesel quality and available energy content.

Octanerating basically gives you an idea of how resistant gasoline is to ignition. The higher the octane, the more resistant it is to ignition, andalso increases to some degree the burn time for any given amount. This is why higher octane is required for higher compression. You want the gas to burn, not explode in the cylinder.Explosions cause knocking which will damage the engine.

Diesel fuel is rated by cetane. Cetane is, for the most part, the opposite of octane. It tells you how volatile the fuel is. In diesel, higher cetaneratings (i.e. more volatile, or susceptible to ignition) the better, but only up to a certain point (roughly 55 cetane). Most of today's injected diesels in motor vehicles require somewhere aorund 45 cetane or higher to perform best.

So, sulfur content and lubricity of LSD vs ULSD has nothing to do with cetane rating. Using cetane boosters in your diesel fuel may or may not help performance...it all depends on the cetane rating of the pump diesel to begin with, and increasing it over 55 cetane really doesn't gain you much if any thing at all (and when I say performance, that does not necessarily mean HP...we're talking smooth running, etc). The amount of energy contained in the diesel has nothing to do with the sulfur content or the cetane rating. All diesel, in its base form has a certain amount of energy available and that amount has already been measured. What will matter are other additives that may add or delete from that base energy content, such as the process for making ULSD removing some of the aromatics and thus lowering energy content.

 

BTCruz, knows his stuff. I beg to differ on one point. ( I may be wrong) I beleive that sulfer is not a lubricant. The reason lubricity is lower in ULSD is the process of removing sulfer also removes some of the fuel's lubricity. Everything else is spot on according to all the information I have found.

 

It is correct, higher sulfur content = higher lubricity in the fuel. The processing to make ULSD strips aromatics which lowers energy content per given quantity as well as the desired result of lowered sulfur content. The loss of lubricity due to lower sulfur content is replaced with other chemicals. Whether or not aromatics are added back in as well seems to be the unknown part.

I would not be surprised if oil companies do not bother to try to replace the lost aromatics unless the absence of them means poor fuel quality and poor running characteristics. I say that because lower energy content means lower mileage which equals more fuel sales......it's always about the money :-)

E85 (the high alcohol content gas used as the alternative fuel for "flex fuel" vehicles) may be a little cleaner burning, but several things are for sure. It's hell on an engine, has a lower energy content and currently costs more to make than regular gas. Ethanol is expensive to make, no matter which method you use, although progress is being made in ethanol production from waste, wood pulp, and other non-standard means. Still, it's going to take a while until that technology matures and even when/if it does, do you really think the price is going to go down simply because it's cheaper to make then? I seriously doubt it. I mean come on, the last gas hike was the result of this year's hurricane season predicted to be more active than usual. Fortunately, it seems that prediction was incredibly off the mark, but did the prices revert back to the previoulsy lower price? Heck no.

BTW, thanks for the compliment, but I'm certainly no expert. I've learned a little about fuels in general but oddly the reasons I researched the information and learned has nothing to do with my CTD. I fly a powered paraglider and the discussions on the groups often talk about the use of aviation fuels in our little 2-stroke engines. The reasoning given is often incorrect and I know this, butI needed to learn more about the specifics in order to debunk the myths being passed around in the PPG circles.

 

BTCRUZ thanks for all the info, very detailed. That's what I like about this forum, lots of very knowlegable and friendly people.

 

I just switched over to ULSD B20 and I'm not adding anything to it (PS,Drew's Brew, Etc.) I aleady see a 1 MPG increase (over regular diesel with additives) just driving around town and it is much quiter.I'm going on a trip this weekend with the 10k horse trailer. The last time I made this trip I went up a 3-4% grade for about 3 miles and got the EGT's to 1450 (only for a breif second and backed off when the alarm went off). I'm curious to see how things go (power, mileage, performance)on the ULSD B20.

 

[/align]
[blockquote]
I thought with the ULSD they still have mixed in lubricants for the fuel systems. Is it necessary to mix in 2-stroke oil or just plain ULSD will be fine? Does 2-stroke motor oil hurt the engine?[/blockquote]