Why diesel engines are better vs. gas?

[danmcguire]

Although I have owned my 97' 2500 for 3 years and pulled a lot of happy miles on it pulling our 31' 5th wheel, there is a lot about diesels I don't understand. Why do they hold up so much better and last longer than gas engines? Why can a diesel run simpy by compressing it's fuel until it combusts and a gas engine (gas being much more explosive) needs a spark plug to ignite it? And lastly, why does a 215 hp diesel put out so much more torque than a comparable gas engine with same rear-ends, etc. ? Thanks for the info.

 

[WadePatton]

a stab at an answer or two

Durability. Gassers last longer now than they ever did because fuel systems now are much more precise than they were. The big factor that made gassers junk after 100k back in the carburetor days was excess fuel in cold operation. (I recently sold a half-ton gasser with 329,000 miles on it with good compression and emissions) Gas is a fantastic solvent and all the unburned fuel from "choked" operation (manual or otherwise) washed the lubrication out of the cylinders. Lead used to take care of the valve seats, but then we decided to stop using that. And it took a while to get that problem fixed.



Diesel has always (fer a long time) been more precisely delivered to the engine --especially at startup-- as the injection system controls the ignition timing, resulting in less cylinder washdown. And diesel is less of a solvent.



Diesel engines also must be designed sturdier to cope with the stresses of compression ignition. Heavier block/heads more head bolts, beefier rods, etc add longevity. That's why diesels have been the standard in the trucking industry forever--nobody notices a few hundred extra pounds up front when you're grossing 70k. Also FWIW the inline six dominates the OTR rigs.



Although gas is spark ignited and diesel is compression fired, diesel has a higher energy content. Add the efficiency of a turbo system to that and you get better fuel economy for similar power outputs.



Torque questions I'll leave to a real expert like Joe D or somebody. But notice that a I6 diesel produces more torque than a V8 diesel.



Gas engines can ingnite by compression, but it's usually by accident and destructive to the engine.



Rearend has nothing to do with the amount of torque developed by the engine. It simply changes its direction and rate delivered to the axle.



You real engineers and such feel free to correct me. I got most of my learnin' under the shade tree. Ole #2 smells better than the unleaded anyway--well except for racing gas.

 

[mopar2ya]

diesel

hello, talking about diesels lasting so long,2600 rpm's on 1 st gens,3200 rpm's on 3rd gens, cummins engines, gas engines turn up to 6500 rpms, diesel is 147000 btu's, gas is 125000 btu's,v8 diesel's have a shorter stroke,than i6 engines, longer stroke means more torque,thats why a cummins 5. 9 has 460+ fpt and fords 7. 3 has 460 fpt, fords 7. 3 also turns at 3600 rpm's, hope this helps joe

 

[2ndgen2500]

its amazing how much you can learn on here!

 

[ronco]

Torque output

Diesels are capable of making high torque for for another reason. The diesel fuel burns slower than gasoline. Therefore, the piston is further down the bore After Top Dead Center than a gas engine when the mixture has quit burning. This allows the piston/rod assembly to exert more leverage against the crankshaft. The result, high torque.



ronco



Read the board, I just learned this recently myself.