Quote:
Originally Posted by autoteach
Once again, effects of CR on power
Engine Compression Ratio - Tech - Popular Hot Rodding Magazine
Now, you dont have to believe it at all. In fact, you dont have to read it. But ignoring facts doesnt make your imagination reality. That is only unfortunate for you. Diesel and gasoline engines benefit greatly in their efficiency from higher CR's. |
Okay, then. Let's take an example, using the numbers presented in that article you so thoughtfully provided. Let's go from 9:1 to, say 16:1. 16:1 is a rather low compression ratio for a diesel, but it should work for illustration purposes. Increasing the compression ratio in this manner, according to the article, results in about an 14.5% theoretical increase in the amount of useful power extracted from burning the fuel. Conversely, that could also be thought of as saying that the engine should be able to use 14.5% less fuel to achieve the same output as before. Now, if you want to be nit-picky about it, we could go all the way up to 22:1, and have a whopping 21% or so increase from 9:1. Alternately, you could go with 19:1, and use 18.4% as your percentage.
Somehow, though, diesel engines tend to get more fuel economy than what can be accounted for by merely bumping up the compression ratio. While I admit that comparing a 1.8L gasoline wastegated turbo engine and a 1.9L diesel variable nozzle turbo engine may not be totally kosher, the fact remains that the 1.9T, at 19:1, gets about 36% better fuel economy than the 1.8T, at 9.5:1. Clearly, 36% is better than 14.5% or 18.4% or even 21%. And, no, variable nozzle technology is not that superior to wastegates, so as to cause the remainder of the fuel efficiency increase.
Therefore, not all of the fuel economy gain of a diesel over a gasoline engine is due simply to compression ratio. Other factors play a significant part, particularly throttle losses.