This thread is dedicated to carrying on a conversation on the differences between our two favorite fuels. Let it be stated that neither diesel or gas are "better" engines, but there are proper and improper uses for each.

Steve VW Posted 09-13-2011 06:52 PM
The biggest difference between a diesel and a gas is that that diesel never runs part throttle. (There is no throttle!) Since the worst manifold pressure a diesel sees is ambient pressure (no vacuum!) each cylinder brings in higher density air and can therefore burn its fuel more efficiently. Gassers always have manifold vacuum and therefore each cylinder gets lower density air. This, along with the higher heat content of the diesel fuel itself contributes mostly to the better performance of diesels (esp at part throttle) This is why turbo/super chargers work so well in gassers (and will boost diesels when above ambient as well)

The longevity, rpm/torque, and heat issues are the result of mechanical design. (these are all piston engines after all) Longevity: diesels are heavier than corresponding gassers. Bigger bearings, heavier castings, usually lower rpm. Heat: bigger heavier blocks, more cooling flow, bigger radiators. rpm/torque are largely related to bore/stroke ratios, with the long stroke engines (ie diesels) making more torque. The gassers are designed to be lighter, short stroke, faster spinning and higher peak hp with heat and durability issues at high continuous outputs. Longer life, more torque, higher fuel content and efficiency win over initial cost every time for commercial and heavy applications.

You're right this should have been another thread. My main point was that the diesel/gas choice for the 86 Regal was not strongly favoring diesel based on the existing options for that model. Neither is especially suited for heavy trailers, as you correctly point out. Didn't mean to confuse.

Steve,

I consider the biggest difference between diesels and gas to be that diesels use compression to fire off the fuel in each cylinder versus gas using an electronic system (spark plugs).

Diesel fuel has more energy content than gas, that is the main reason they get better mileage. Diesels DO have a throttle, but it regulates fuel amounts through injectors rather than the use of a throttle plate regulating air flow as in many gas engines. This is why diesels have little natural compression braking (not to be confused with the ignition/piston compression). A gas engine becomes a compressor when the throttle plate is shut. A Jake Brake on a diesel also can make the diesel act this why be shutting the intake valves.

A normally aspirated gas or diesel brings in ambient air pressure, only a turbo/blower can boost ambient pressure brought in for combustion. Compressed air is denser and has more oxygen to accelerate/enhance combustion.

Diesel engines usually last 5 to 10 times longer than a gas engine due mainly to the use of the lubricating fuel and the low RPM of the engine (around half that of many gas engines).

Again, neither is a better design, but diesels are definitely the modern choice for heavy capacity vehicles.

Several issues with diesels are their weight, their cost, their higher soot exhaust and their dislike of idling for long periods where they can build up carbon.

Although contemporary diesels have surrendered some of the advantage, diesels are far simpler in operation and in routine maintenance. Change the oil and filter, treat it to a new fuel filter and a coolant change now and then, and they run forever. Never needs a tuneup, or sparkplug wires or distributor; maybe a set of injectors at 300K miles (usually easy owner fix).

Add to that is the fact that a fuel leak is a fix-and-cleanup problem, not a fire hazard.

Diesels not only enjoy better economy from the higher energy content of the fuel, but also due to the higher compression ratio (which also results in lower exhaust temps - when at 0 boost).

Unknown to most, the Soviet Union in WWII had a long-range heavy bomber, the Pe-8, powered by 4 diesel engines. The only reason most have never heard of it is because the engines were unreliable. When all 4 operated normally, the Pe-8 exceeded by far the performance of the B-17 and approached that of the legendary British Lancaster, despite its shortcomings.

One advantage of a gasoline engine is that you can turn it off much easier than a diesel!
Why are fuel solenoids ( a very simple device) so fricken expensive? Looks like the Onan genset wants another solenoid….