I almost put diesel fuel in my parents’ car once. Fortunately, the diesel fuel dispenser didn’t fit into the little fuel-filling hole; it was too big. I wondered what the hell was wrong until I noticed that I had absentmindedly grabbed the wrong one.
In the report, Una said:
I hate to pick nits (unless I am actually lousy 
), but this isn’t really a nit – it goes to the core of the diesel cycle. A diesel engine does not mix fuel and air and then compress it, as Una stated in the Staff Report. Instead, air only is compressed and the fuel is injected (“direct injection”) when the piston is at the top of the compression stroke.
Thank you for reading the Straight Dope Staff Reports, and we rely on people to nitpick and find mistakes, omissions, and editing problems where they occur, so there’s more of the “Straight” and less of the “Dope”. This editing error which was entirely my fault was pointed out earlier in this thread ( http://boards.straightdope.com/sdmb/showthread.php?t=277183 ). It has been updated on the website, and should show up correctly now.
Diesel can and does gel at cold temperatures. Winter diesel contains a small amount of kerosene to prevent this from happening. (kerosene, which is in the same boiling range as Jet Fuel, is lighter than diesel but heavier than gasoline) As with all things, US government regs have tightened over the years, so adding gasoline to diesel in the winter was probably a good idea 20 years ago, but is probably overkill nowadays. Winter gasoline has a higher vapor pressure because gasoline engines need vaporized fuel to start. Obviously, the colder it is, the harder it is to vaporize a liquid, so refiners add butane to gasoline blends to raise the vapor pressure. Summer gasoline is 7-9 psi Reid Vapor Pressure (RVP) and winter gasoline is 11.5-15.5 psi RVP.
I used to have a caddilac coupe deville diesel. I loved that car.
It used to scare the bejezus out of gas station attendants though. They would freak when they saw me filling up my caddy.
For point of reference, typical octane ratings in the States are 87, 89, and 92/93. As long as your engine doesn’t knock, you’re fine. Generally, using a higher octane rating than recommended for your car will do nothing for you, except put more money in the pockets of the petroleum industry.
Not quite. Some modern electronics will adjust on the fly to low octane, but run the engine suboptimally to do it.
How often would a typical American coal-fired plant need to be warmed up in this way? I can’t picture them shutting a plant down for no good reason, and if power plants aren’t built to be reliable, nothing is.
And, on a similar-but-not-the-same topic, could a coal-fired plant reasonably run on wood? (I’m aware that there are many different kinds of wood. I don’t know any better way to frame the question.)
Coal plants go online and offline for a variety of reasons, both planned and unplanned. I’ll list a few here:
Planned Outages:
Routine maintenance (typically from 1-3 times a year, lasting from 2 days to 6 weeks)
Reduction in demand (such as in Spring and Fall)
Economic dispatch (typically the most common planned reason)
Unplanned Outages:
Equipment failures
Problems with coal delivery (uncommon)
Problems with coal handling (frozen coal, fires, pluggage of chutes)
Emissions problems
Catastrophic slag buildup
Accidental trips (shorts, turbine problems)
Feedwater/cooling water problems (low river levels, plugged intake screens, Zebra Mussels…)
Generally, IME most large coal plants have from 3-10 shutdowns a year, and most small ones from 1 to 20 or more. A large coal plant takes about 6-12 hours to come up from a cold start, depending on the type of plant and the training/efficiency of the operators and control systems. During this time, either natural gas or fuel oil (number 2 or number 6) is used to heat up the furnace and get things started.
These warm-up burners can be rather large, and in some cases can supply as much as 10-20% of the heat of the furnace (and in some occasional cases can supply 100% of the heat). Sometimes, if the unit is having problems with coal, they turn on the warm-up burners during normal operation to cover the lost energy - this is quite expensive, with coal being roughly 130 cents/MBtu, whereas fuel oil can be from 250-350 cents per MBtu, and gas from 300 to 600 cents/MBtu. However, if power prices are running anywhere above $50-$100 per MWh, it’s more than worth it to turn on the warm-up burners and get back any lost output.
Wood can be co-fired with coal, and in fact I am doing a study on a coal power plant that is burning from 5-10% wood chips along with their coal on a regular basis. It can either be roughly ground to about charcoal briquette-sized pieces and mixed with the coal, finely ground and injected into the furnace alongside the coal, or even gasified and the gas and char injected into the furnace. Wood is generally low-energy content per pound unless dried extensively, but typically does well at low heat input percentages. The three main, critical problems with wood burning at coal plants are:
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Finding enough to burn - even a small plant will burn 4-10 tons per hour every hour, and that’s a lot of waste wood to dig up. A single larger plant may require as much as 40-50 tons per hour at 10% heat input.
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Logistics - collecting and transporting the wood is very difficult. Coal has a relatively simple transportation system - you load up 11,000 tons at a time on a train at the mine, and send it on it’s way. Finding a single convenient source in one spot that generates 11,000 tons of wood waste is impossible. Coal has a nice consistency to it, and it’s easy to handle and move - wood waste needs collecting from many different sources (sometimes dozens), needs sorting and pre-crushing, and typically is transported by small trucks. Reliability is also a big problem - some sources have huge amounts of product available, but only at certain times of the year - so you have to plan around that.
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Inconsistency of product - coal varies quite a lot from State to State, mine to mine - but once you take it from the same mine, you get the variability well in-hand. Wood can vary greatly in heat content and combustibility, depending on the moisture and source. Pine bark is very different than particle board, and willow fuel crop very different from railroad ties. Wet fuel crop wood can have heating values as low as 4000 Btu/lbm, whereas dried railroad ties can be as high as 8500 Btu/lbm. Plus you never really know what you’re getting in mixed waste - what heavy metals (chromium and arsenic for treatment), nails and other metal scrap, etc.
Plants that get a good, reliable supply of wood of decent consistency love to burn it, even if it costs more than the coal. Every single coal power plant I’ve been to has everyone I meet, from the owner or utility VP to the bulldozer driver in the coal yard, in favour of burning more renewables. People have this idea about coal plants deliberately dragging their feet on burning biomass and renewables; that has not once been my experience in the dozens of studies I’ve done on coal plants burning renewable energy. Even in the most confidential meetings, where I sign NDA’s preventing me from even saying I’m working for a client, the word in the meetings is “how can we reduce our CO2 emissions? How far can we go?” But it is still amazing how many things conspire to prevent it from happening - anywhere from wood suppliers that suddenly dry-up, wood suppliers that suddenly raise their waste prices by 500% as soon as they find out a coal plant is interested, truckers that suddenly demand $50-$100 an hour to drive a truck loaded with wood, State and local officials that materialize to find ways to prevent permitting of un/loading facilities, local residents that get dollar signs in their eyes and start suing the plant over the increased “noise” and “danger” of moving that much wood into the plant, schools sue over traffic from the trucks, the EPA comes by to crack down on potential trace element emissions from wood, and yes, even environmental groups will come by to have a regular Festivus of why burning trees for any reason whatsoever, even if the trees are grown for the sole purpose of providing green energy, makes the plant owner worse than Hitler. And somehow these people seem to have unlimited funds for lawyers…
It’s amazing how sometimes many people that are supposed to be part of the solution turn out to be part of the problem, and it’s the coal plant and the utility that get the blame.
Well, I certaintly didn’t expect that last bit, but I’m glad you threw it all in. It’s encouraging that coal plant owners and employees are interested in making our power generation system that much friendlier to the environment, even if the American reality seems to abhor a clean power plant.
Green nuts who hate a renewable energy source? Bah. More morons for the marching.
I certainly can’t say it’s all, or even most plants that are this interested in wood and/or reducing CO2 emissions. In fact, my experience may be skewed a bit in that generally when I get called out, the plant has already made a decision that they want to do something about CO2 emissions. However, I get a lot of calls and make a lot of trips, as do my competitors, especially to the larger plants. So it seems like a large amount.
Other than wood, are there other agricultural waste-type fuel sources that can be co-burned? Corn stalks, chaff, etc? I know that large dairy operations have huge supplies of manure, which was used a fuel source on the prairies. There would be a whole other problem of emissions, true, but if it’s cheap…?
Scads of them, each one having its own specific problems and benefits. Common ones include switchgrass, miscanthus straw, and corn husks/cobs/waste. Sugar cane waste (bagasse) is commonly used as fuel, and you often get odd items such as olive stones, orange peels (from the orange juice industry), nut shells, and rice hulls.
Most manure does not work all that well on large-scales due to the problems of collection and drying. Turkey/chicken/poultry litter (waste mixed with straw) solves some of the collection and dampness problems, and there have been a few threads in GQ where people have talked about cracking process to reputedly make cheap oil/power from them. AFAIK none of the processes is currently running in actual production mode, but I could be wrong. Sewage sludge, when dried properly, can be used in coal boilers along with the coal, and is/was at several sites in Europe, and I think a couple in the US.
(for more on this, you can read EPRI Report TR-111487, the “Opportunity Fuels Guidebook”)
The power plant I was at last month burned corn husks and corn cobs, and really liked doing it, until problems with incredibly sticky ash plugged parts of the boiler so much they had to cancel the test, come offline, and clean the boiler. That cost a lot of money. I’ve worked at plants that pipe in landfill gas, sewage treatment plant gas, miscellaneous wastes such as automobile “fluff” and diapers (seriously…). I’ve even done a study a while ago with others, sponsored by the UK government, where they seriously considered burning waste animals from BSE (Mad Cow) and “Hoof and Mouth” culls in power plants. That was almost surreal, and somewhat disturbing to work on (some of the main problems were exposure to the corpses, transport of the corpses, and public fears over BSE escaping from the power plant).
Okay… First let me preceed this saying that waaay too much about TDI engines. Only academically speaking though. I have one and I used to spend SO much time reading learning about different fuels etc. Now, most of this stuff is covered on Freds TDI Page.
There is way too much info to go through on that sight. But I was such a nut, that at one point, I ordered an Airflow sensor from Germany that was made for use on a Mercedes Diesel, because it was of higher quality and cheaper than the Pierburg sensors. Mine is made by Bosch. It hasn’t gone dead yet like all of the Pierburg sensors… Okay maybe you will all trust me now.
Firstly with respect to the nozzles. There are two different kinds of Diesel pumps in the good ole U S of A. Firstly you have the ones that the heavy trucks use. They are usually around back and are really dirty. However, there are also the “Auto Diesel” Pumps that are sometimes integrated into the normal gas pump. I didn’t read what the original staff report was referring to, but I have never seen an “Auto Diesel” Pump (that is to say one that is integrated in the same pump as the other three gas pumps.) that had a large nozzle. Every single one that I have seen has the same size nozzle as the gas pumps. I have also never seen a “Big Rig” pump that had a small nozzle. In fact, in my owners manual for my TDI it mentions that the wide pump nozzle is in case you can’t find a diesel pump that has the smaller nozzle. The big pumps go really fast and create a lot of foam that keeps you from being able to pump normally. it always shuts itself off.
Also in the US you can run any kind of untaxed fuel. Well, I wouldn’t say that. I mean you can run on any kind of homemade fuel. You can’t run offroad diesel. But you can run on Straight Vegetable Oil. This is what a lot of people do.
Just to be complete, you can burn any kind of homemade fuel in your car, but you can’t sell the fuel to anyone else (unless you get it tested, certified, yadda dadda).
In the Marines we had the International Harvester TD15 bulldozer.
It started on gas, then, after pulling a lever when it warmed up, it would shut off the spark plugs, and put the diesel pump in gear.
That simple, it worked fine, except it lacked the horsepower of todays diesels…
Because they were the same damn size and on the same damn island, that’s why. :mad:
Interesting discussion. Do you know that a gas engine can be built to accomodate diesel fuel, or for that matter just about any kind of fuel? Here’s an article explaining a new technology. :smack:
I have a cousin who used to work at the fuel dock at King Harbor in Redondo Beach, CA. He said one time a careless boat owner–whose vessel had a diesel engine–stupidly had the cousin put gasoline in it, then realized too late what he had done.
My cousin said, “Well, now you’ll have to wait here while I drain the gas out of your diesel oil tank.”
I shudder to think what the alternative would have been. 
Definitely crossing over into spam, now. Note the bottom of the newspaper article: