Aquaduct
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Re: Diesel vs gas......................
For more information, do a search online for bio fuel, and you'll get the scoop! In fact I'm thinking about going into business, although, remember the guy in the early '80s who made fuel from garbage? (Probably ethanol?) He was on 60 Minutes. He had had attempts on his life.....and where is he now? Linda Not to take the wind out of your sails, but I'm a diesel engine engineer. Yep, biodiesel is an established technology. There are some technical differences with regular diesel that aren't that significant in a modern engine. It's safe to say that good biodiesel is a satisfactory replacement for diesel. That said, most engine manufacturers will only warrant an engine on a fuel that is, at most, 5% biodiesel (technically called B5). This is primarily for 2 reasons: 1. The biodeisel industry can't make that much anyways. 2. Quality control in the biodiesel is hit and miss. There are good biodiesel suppliers but there is a substantial amount of bad fuel. A big slug of bad fuel will destroy the injectors, generally the most expensive components on the engine, and/or other parts. This comes from the fact that there are bunches of folks brewing stuff with less than critical attention to or understanding of the subtleties of large batch chemical processing, which is a whole different ballgame from refining petroleum or brewing a batch in your sink. So at B5, we're comfortable that crummy biodiesel won't exist in enough concentrations to damage the engine. Y'all want to brew and use your own, that's fine. You break it, you've bought it. If you want to sell to others, be sure your product liability insurance is paid up just in case you screw up a big pot.367Views0likes0CommentsRe: Diesel vs gas......................
Wow! That is alot of math. It will take me a while to go through it all. In actual practice I can understand what you are saying. I have talked to many people driving or hauling the same amount of weight,22,000#-26,000# GVW or GCW, and as one guy said,"It doesn,t matter what engine I have, I get 8-9 mpg." No one in our groupe pulls away from the other. Makes you wonder if diesels are worth the money. Roger Don't get either Bert or I wrong, diesel has one indisputable advantage, fuel economy. A diesel will get 20-40% better mileage on the road and use 50% less fuel when idling. Combine that with cheaper fuel most of the time and that's pretty significant. On the flip side, they are going to be heavier and more expensive. But, if you tow a lot, there is a definite economic incentive for diesel. That's why commercial rigs use them. And, unfortunately, the subscripts and superscripts that I used didn't translate to this format at all. The Sv2 in the road load formula should be Vehicle Speed (S subscript v) squared. If some things confuse you, I'll be happy to clarify (I'm sure Bert will too). And just remember, power and torque are 2 faces to the same coin, mathematically, so comparisons based on one will carry over to the other. For instance, I was reading a review of a motorcycle I like. The writer commented that the extreme acceleration was due to a torque curve that started at something like 100 lb/ft of torque and stayed flat to 1800 rpm. Good low end torque. True enough, but look at what happens to power. At those engine rpms, the power shoots up from 15 hp to 34 hp in 1000 rpms (I think peak power comes on at 6000 or 7000 rpm). This is for an 800 lb. bike with negigible rolling resistance and miniscule air resistance. The power required to move the bike is very small. Either way you look at it, torque or horses, it's a rocket. Again, neither Bert nor I claim diesel or gas have absolute advantage. There are pluses and minuses and to each his own, depending on your needs and preferences.420Views0likes0CommentsRe: Diesel vs gas......................
Just one question. My truck and trailer have a GCW of 25,000#. I can drive down the interstate with the cruise control on,in overdrive, and not worry about it downshifting. It only has 250hp. about 100hp less than the GM 8.1 gas and the ford V-10 gas. Why? Because it's not really that big a deal. A loaded 80,000 lb. tractor/trailer rig takes only about 200 hp to run 55-60 mph. Of course, with that much wieght, the grade penalty can be substantial, but, depending on how fast you run, the rest of the system, and the shape of the power curve, 25K should be do-able with 250 horse. Of course if you had more system data- power curve (or torque curve, it's easy to get one from the other), gearing, effective tire diameter, maximum rig height and width, cruising speed, rpm at cruise, automatic/manual- I could diagram it for you. I could also diagram it for any other powertrain that you'd like to compare it to. In fact, I've given the calculations to other forum members, maybe they've got the time to share them.338Views0likes0CommentsRe: Diesel vs gas......................
I'll add the following with a qualification first - I'm a degreed mechanical engineer. This topic is the stuff I studied in school and it's what a lot of BSME's do for a day job. What makes you think qualifications count? (Just funnin' ya. I'm a powertrain engineer and most people don't listen to me either). Just to refresh your memory and put to bed some minor details; Torque is a force. Like any force, it can be present without actually accomplishing anything. I can push on the side of a building with my hand and still apply a force without moving anything. A force that moves something over a distance creates work. Work done in a certain amount of time is power. Power and torque are mathematically related. Hp = torque x rpm/5252 in non-metric units. The significant difference is that power is consistent throughout the engine/drivetrain system. Torque changes with gearing. A moving vehicle requires a certain amount of power to move it at a certain speed (distance per unit time). It's a relatively simple formula that starts low at slow speeds when you're only overcoming rolling resistance and increases rapidly over about 30-40 mph as wind resistance builds. Any grades will tend to increase those requirements pretty substantially. Gearing also forces the engine to operate at a particular rpm for a specific speed. Given some corrections for drivetrain efficiency, if the engine can deliver the required power at the given speed, you'll continue at that speed. Acceleration is actually a function of how much more power is available than is needed. But remember, torque and power and mathematically joined at the hip. All these calculations can be done using engine torque, but the math ends up being more of a PITA. If you actually sit down with engine and drivetrain system data, you'll realize that anytime someone talks about great performance due to torque or power, similar math will get you to the same realization with the other. Torque's real significance is at the only place where power doesn't exist (at the wheels anyway) which is when the vehicle is not in motion. Torque is significant in getting the wheels rolling or "startability" as it's called. The efficiency and durability advantage of diesel doesn't tell the entire reason for thier popularity in commercial trucks. The fact is that diesels have yet to play by the same emissions rules as gas. That fact will potentially shake the heavy duty industry in the next decade as "fuel neutral" emission rules and low sulfur diesel fuel rattle the commonly held assumptions of diesel towing superiority. Diesels really gained a heavy duty advantage over gas with the advent of turbochargers, allowing them to get substanial power to go along with low end torque (a byproduct of extra rotating masses and lower rated rpms). They were no longer "all grunt and no go" and commercial trucks could get fuel efficiency and speed making them economically superior. 2002 brought substantial emission reduction requirements met mostly with EGR and CAT's Miller Cycle operation. Fuel economy and price have taken a non-negligible hit and system durability has been affected somewhat. 2007 will virtually eliminate smoke emissions and will introduce aftertreatment systems for the first time, again impacting cost, economy, and system durability negatively. 2010 will virtually eliminate NOx, again with predictible results. And all of that doesn't take into account the shift in fuel prices that can occur if diesel cars become as popular as they are in Europe once the emissions get cleaned up. I mean, just look at how much howling goes on when the heating oil season kicks in. This is not to say that diesels will disappear, but it will even the field for gasoline which will continue to improve. I've seen knowledgable industry predicitions that diesel will lose its effective economic advantage by the middle of the next decade. Do I agree with the predictions? I do heavy diesels and I don't think things are that dire, but the preposterous notion that either cycle has a God-given superiority would prove to be economically fatal. Yep. Right now diesels give better fuel efficiency that can offset the extra cost with solid performance. But I can buy gas at no less than 3 stations within 4 blocks of my house. I haven't found an in-town diesel station yet. And my wife doesn't like diesel. And I don't tow that much that I going to recognize much savings, if any, long term. At the end of the day, buy what you like and what suits your job. It's not a simple one dimensional question and simple platitudes serve no purpose.338Views0likes0CommentsRe: Diesel vs gas......................
I am curious, though. Why can't you inject the fuel directly into the cumbusion chamber in a gasser the way you do in a diesel? Is there a problem with the way it would burn? I seem to remember reading that detonation is basicly a really messed up flame front instead of a smooth one. Would direct injection of a gasser cause that kind of a problem? Yes you can. It's been a while since I really paid much attention to the gas side of the world, but I think that there are at least a couple GDI (Gasoline Direct Injection) systems on the road today. I'm thinking a couple Japanese makes and a couple super-luxury European cars. In fact I was reading about some ideas of using GDI to develop a gasoline heavy truck engine for an anticipated economic shift away from diesel in the next decade and a half. Actually, the concept was fairly sucessful in the pre-carbeuretion days (1930?). There are a couple fundamental issues with it even before you get to reliability questions. First, a diesel has to use compression ignition due to the higher flash point of the fuel, so it's not as simple as applying diesel principles to gasoline, although there are a number of parallels. The advantage of current homogenous port injection is primarily one of speed. When you burn the mix, you try to get the most pressure rise out of the combustion as possible. So you initiate combustion just before TDC so the fire is really burning and creating pressure to push down on the piston as it rolls past TDC. The problem is that as the piston moves down, volume is increasing lowering pressure and temperature. So it becomes a race to create as much pressure as possible before the moving piston neutralizes it. Fuel only burns as a vapor, so if it's mixed and a vapor before entering the cylinder, it burns faster than having to diffuse, vaporize and then burn like in direct injection. Faster burns mean more power, which is the inherent strong suit of gasoline spark-ignition port-injection sytems. (NOTE: Before all the diesel fans get all grumpy, I'm not saying gassers make more power. It's an inherent advantage of the combustion cycle which can be overcome with things like turbochargers, just like fuel economy is an inherent advantage of the diesel cycle.) Port injection also runs at stoich which makes emissions easier to manage with TWCs. Direct injection gives finer control over the cylinder mixture so you can create rich zones around the spark plug that will let you run leaner than port injection. Something like 40:1 as opposed to 17:1 for a port system which is where you'd start to lose your ability to ignite reliably. More precise mix control also lets you run at lower rpms (ie.- 600 idle vs 750) and the cooling effect of the direct injection of fuel in the cylinder lets you run higher compression ratios without knock. All this adds up to diesel-like fuel efficiency on regular gas. However, the same emissions problems of diesels crop up. NOx is high and there can be HC problems is the mixing isn't right. So now you're into higher injection pressures, more EGR, and the ever-challenging NOx reduction in O2 rich environments. Like I said, I believe it's out there. I think one system is even set up to run both ways. The intake ports come into the cylinder in such a way that they can inject in the compression cycle for GDI operation and fuel economy, and then inject in the intake cycle for homogenous mix and power. Something says Isuzu or Mitsubishi. They've also got a Lean NOx Catalyst (LNC). EGR is used to control knock at the higher homogenous compression ratio. I think at some point, you also have a problem with too much EGR which then requires a high energy plasma or laser ignition system. But I don't think that's part of the systems on the road. By the way, did you ever get the note I sent you?374Views0likes0CommentsRe: Diesel vs gas......................
Diesels and gassers work on exactly the same principle, so your findings are not surprising. I have to admit, though, that I have wondered what would happen if you took a gasser and adapted a fuel delivery system from a diesel for it. One of the biggest problems a gasser faces is detonation. Since the fuel system on a diesel engine delivers the fuel to the cylinder when it is needed, it seems that detonation would be avoided. Anyone know if that has been tried? Bert No, they're different combustion regimes. Gassers have a pre-mix in the intake manifold and then they burn with a homogenous flame front. Diesels have stratified, non-homogenous combustion. Little burning droplets, if you will. It means that you're fighting very different problems. As far as air/fuel, these days you're limited by emissions requirements. The extra heat of lean combustion forms NOx. Rich mixtures leave HC and CO in gassers and soot (particulate matter) in diesels. Gassers have the miracle of Three Way Catalysts to control emissions, but to do that, you've got to stay very close to stoich. Basically, the TWC switches very fast between oxidation (HC and CO) and reduction (NOx) regimes to stay very clean. You could lean out a gasser to get better fuel economy, but you won't have a prayer of a chance of emission certification. Since you get the proper mix prior to ignition, it's easy to run at stoich. Diesels have a different story. Since you're injecting fuel droplets, you've got to run lean to make sure you've got enough oxygen for combustion. You've also got to have as small a droplet as possible, thus huge injection pressures. Without enough oxygen, the droplets only burn to little "charcoal briquets" which is known as particulate matter. So in reality, you can only run to about 18:1 before you belch too much black smoke. I think that momentarily diesels can even exceed 100:1, but most of the time these days, you're about 18-25:1. That makes it real tough to get catalysis to work. If you're lean, you're producing NOx. To get rid of NOx, you need to reduce it or take the oxygen away. Tough to reduce things in an oxygen rich environment. It's kind of ironic really. As technology progresses, gassers try to figure out ways to run lean for better fuel economy. Diesels try to figure out how to get to stoich for emissions reduction. It makes for a fun work day!370Views0likes0CommentsRe: Diesel vs gas......................
Aquaduct, The numbers for the Ford Superduty trucks have changed for the 05's. The V10 is no longer 310HP, and they can now be equiped with the Torqshift. Nobody still seems willing to answer the question Joe posted though... he 2005 320HP 8.1 Suburban has a 3,000 lb higher tow capacity than the 335HP 6.0 Suburban You'll notice that Joe never bothered to answer my question. In 2004, the V10 automatic has the same GCWR and a higher tow rating with lower horsepower and torque. At least I'm saying that there are many other factors to consider. Really, I'm even bolstering a side of his argument by pointing out that it ain't all about horses either. Joe just makes grandiose claims that "every manufacturer" bases tow ratings and GCWR on torque and then just dismisses everyone who disagrees as profoundly stupid. Then he changes model years. And then he misquotes you and makes fun of you in every thread he's got an opportunity to. Frankly, I don't know anything about the 2005's. Don't keep up on the magazine reviews. I can only work with what's published at the moment. If you want to buy Joe's arguments, feel free. In the long run it won't matter. Gas or diesel, similar vehicles with similar engines will give relatively similar towing performance. Personally, he bores me.370Views0likes0CommentsRe: Diesel vs gas......................
In fact, I think Ford gives higher tow ratings (by 500 lbs) in the Super Duty pickups (F250/350) to thier V10 over the PSD despite lower peak torque AND peak horsepower. Ok, it's time to cut the BS. The 2005 Ford 325HP 6.0 PSD has up to a 7,000 lb higher GCWR than the new 355HP V10 in the same truck with the same trans and with the same axle ratio or even when the V10 has a higher axle ratio because of much more torque. The 2005 320HP 8.1 Suburban has a 3,000 lb higher tow capacity than the 335HP 6.0 Suburban because of much more torque. This forum needs a bs protector big time. Good Lord, Joe, don't you ever tire of being a jerk? What I said is absolutely true. On the Ford website, comparable 2004 F250/350 trucks with automatic transmissions have equal maximum GCWRs and the diesel has 500 lbs less tow ratings probably due to the extra wieght of the diesel. And the V10 only has 310 hp. And less torque than the PSD. So what that they have different rear ends? That's the point. If you've got horsepower, you can gear for torque. Duh. Looking further, this holds true through F550 with one exception that requires some special differential. And as near as I can tell (I haven't made Ford specifications my obsession like you appear to have since I worked there 6 years ago and I've never cared about GM specs), the V10 and the PSD have different transmissions, 4-speed vs. 5-speed automatics and 5-speed vs. 6-speed manuals. Now manual transmissions are another story, where the diesel has significantly more maximum GCWR than the gasser. That difference isn't really about engine torque (although I suspect it is at the root of it), it's about a manual vs. automatic transmission. And before you read something stupid into the above statement, I suspect that an automatic's relative inability to handle torque is at the root of this apparent anamoly. A manual transimission lets the vehicle take advantage of the horsepower and torque of the diesel. Basically, they have to derate the vehicle to keep the automatic transmission alive. And in the end, so what? The point is that it is a system. Anyone who buys a tow vehicle based on either maximum torque or maximum horsepower is stupid. My example simply shows that it is possible to buy a vehicle (and a wildly popular RV TV) with better tow capacity and lower hp AND lower torque. For someone who needs help understanding tow capacity and the differences in vehicle capabilities, that's an important point to make. I certainly don't need to prove anything to you. So, what Ford Superduty pickup will tow best? It all depends.370Views0likes0CommentsRe: Diesel vs gas......................
Do you know how much of an effeciency increase a properly installed turbo will get for a gasser? I was reading a "wheels" article a while ago that claimed that almost any gasser can gain around a 20% jump in efficiency when a turbo is installed, but that sounds high to me. Depends what they mean by efficiency. Volumetric efficiency of a normally aspirated SI engine will be about 80-90%. A turbo will bring that up to at least 100%. So that number would seem valid. If they're talking about fuel consumption, you wouldn't get anything (assuming you're constrained to running at stoich with a modern, aftertreatment-equipped engine). The higher air flow would have to matched with the same relative amount of fuel. However, if you were an engine designer and were using a turbo to get similar horsepower from smaller displacement, than you'd get the same fuel consumption at high load, high speed regimes of the turbo and probably a 10% reduction in fuel consumption elsewhere due to the smaller displacement. Again, I only deal with production type engines that have to go into factory vehicles so I'm not as well versed on the ins and outs of racers and other vehicles without emissions and fuel economy contraints. So maybe someone else will prove me uninformed. That would be cool.423Views0likes0CommentsRe: Diesel vs gas......................
Also remember that gasoline engines are knock-limited, so you can't get anywhere near the boost advantage that you can with a diesel. Something like 10-12psi for gas vs. 30-50psi for diesel. That's why more gas engines aren't turbocharged. Not as much bang for the buck.422Views0likes0Comments
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