Diesel vs gas......................
OK folks, there have been a few to many diesel vs gas threads that have shall we say gone to "Hell and a hand basket"! So if all of you would put in you BEST, no flaming reasons for going gas vs diese...
Forum Discussion
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!
