Originally Posted By: 38sho
a diesel is still a reciporating engine, if they can change their designs from whimpy N/A workhorses, to [censored] near impressive turbocharged beasts..... same can be done with a gas engine...... all in how they build it.
Actually, that's not quite so simple to do. Diesel and gasoline engines operate on a fundamentally different thermodynamic cycle. Diesels approximate constant-pressure combustion, gasoline engines approximate constant-volume combustion followed by adiabatic expansion (in practice there's some overlap because neither cycle is ideal). Diesels CANNOT suffer detonation, because the fuel doesn't even appear in the cylinder until its time for combustion to begin. You can feed a diesel air at temperatures and pressures that would cause a gasoline engine to self-destruct instantly through detonation. Also, the constant-volume combustion of gasoline engines puts a much larger impulse loading on connecting rods, bearings, etc. at very high power settings/low RPM because so much more of the combustion cycle happens right at top-dead-center than in a diesel, where the burn runs through the a large portion of the piston down-stroke. That's why diesels can be designed to produce so much more low-end torque without self-destructing.
Compare the pressure-volume diagrams. Gasoline:
http://www.qrg.northwestern.edu/thermo/design-library/otto/Otto-Pv-diagram.gif
Diesel:
http://www.qrg.northwestern.edu/thermo/design-library/diesel/Diesel-Pv-diagram.gif
The sudden pressure rise at a fixed volume is the limiting factor in the Otto cycle.
The upshot of that is that diesels can run 100% of the time under full turbo boost. Gasoline engines can't. At least not easily and not with the same amount of boost. As I said, depending on how the direct injection cycle is timed, the Ecoboost may overcome some of that. But not all of it- its still going to be fundamentally an Otto-cycle engine, best suited to short bursts of 100% power and long periods of 80% power is better served first choice by a turbo-diesel, second (lower initial cost being the attraction) choice by a large-displacement, relatively low-compression, normally-aspirated gasoline engine.
Don't get me wrong... its been a long time since an engine design has made me drool like the Ecoboost does. I just think an actual WORKING truck (as opposed to a sport truck) is not the right place for it. Just like no one did a lot of heavy towing with a supercharged Ford Lightning or a Dodge SRT-10 with the aluminum Viper V10.