TN Post Wh*re
Join Date: Apr 2002
Location: Bellingham, WA
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Well, lets be honest - Diesel engines, especially turbo diesels, are dirty dirty engines. They don't conform to the normal output of a gas engine and as such are exempt from emissions testing as CO and Nox are different. That isn't to say that they aren't dirty polluting engines.
For those that don't know - there's actually a reason that a diesel engine outputs all that black smoke.
A gas engine is regulated by the throttle body. The throttle body lets air in. A gas engine will pull air in (or forced induction, air is forced in) and the engine electronics (or carb based on vacuum) will determine the amount of gas required - keeping it within an appropriate range of stoich, while creating needed power and not running too lean. This system works and gas engine can run at a higher RPM - they are ignited by spark plugs (electronically). They have a controlled flame-front and as such, that's why we regulate the air coming in. As such you hit the "gas" pedal, which the throttle body snaps open and there is a very slight delay in the amount of air vs gas (this is lean) - then the electronics kick in and add additional gas.
A diesel works almost in reverse. There is essentially an open amount of air available and hitting the throttle actually controls how much diesel fuel is being pumped into the engine, regardless of how much it "needs" given the rpm/air available (or being pushed in). Further diesels do not rev as high because they do not use a controlled flame front - it will self ignite based on temperature and compression. This is called "ping" or a chaotic flame front - meaning the spark can occur anywhere in the combustion chamber (this can happen in a gas engine and it's very bad). In any event - diesel engines dump black fumes out because when the driver hits the "gas pedal" the system pumps more fuel through the system before the engine actually needs that much fuel.
A turbo system will always require more fuel - be it a diesel or a gas engine. It's very common for diesel guys to up the turbos and as such require more fuel - this allows them to increase power and tow more (or tow the same amount up steep hills without issue) - usually these increased setups have a computer that controls how much fuel can be delivered or what "level" the driver wants the power to be at (based on turbo pressure and fuel delivered) - coal rollers can essentially manipulate it to dump excessive unburned fuel out the tailpipe.
To say a diesel is cleaner than a gas engine is like saying a stagnant pool of water in the jungle is safer to drink than ocean water.
1) Frame-off "Rusto-Mod" FJ40/350/350 2) 2001 Lexus LX470 3) 2017 Prius V4