For ages, derided as slow and more noticeably, filthy, automotive diesel engines went in for a big makeover over the last couple of decades.
Common rail injection is a form of fuel injection that can spritz diesel into the cylinders at very high PSI in very precisely controlled bursts.
That kind of control of the amount of fuel, and how often it sprays into the cylinder, combined with turbo charging Revolutionized both the power output and CO2 emissions coming out of diesel engines starting in the late 90s.
Around 2006, ultra-low sulphur diesel fuel became the norm in the UK, Europe and US.
It reduced the dirty sulphur content in diesel fuel from 500 parts per million to 15.
Taking that out reduces the energy content in to the gallon of fuel slightly.
But primarily sets the stage for a key pair of cleaning technologies to kick in.
Selective Catalytic Reduction puts a special catalytic converter in a diesel car's exhaust system.
Inside that can is sprayed a mist of urea fluid that combines with heat and the special metal surfaces in the catalytic converter for a reaction that scrubs diesel emissions way down in several key areas.
The down side of SCR is that you have to add this expensive plumbing to the car's underside and refill the car's supply of urea fluid from time to time.
Typically at 10 to 15,000 mile intervals.
Some dealers will do it for you as a courtesy during routine service, or you could do it yourself with a bottle of the stuff from Amazon or an auto parts store.
It's like adding washer fluid, but it's one more thing to fiddle with.
The TDI from Volkswagen.
Right about now, we should have smelled something fishy.
VW was meeting stringent, new US diesel emissions standards from 2009 on.
Without SCR on most of its diesels, which seemed like a trick no other car maker could pull off.
As we now know, they weren't pulling it off either.
These events are deeply troubling.
Retrofitting one of these bulky complex SCR exhaust systems and urea tank
To the effect that TDI VWs and Audis out there is one way VW may have to address the current cars that are on the road and violating emissions standards.
But what if diesel exhaust could be cleaned up before it's even exhaust?
That's what they're working on at the Oak Ridge National Labs where they're developing diesel engine tech that injects fuel into the cylinder early in the combustion cycle.
Something which almost defies the definition of a diesel.
That along with a new breed of sensors demands the fuel timing precisely based on nuanced real time measurement of cylinder pressure could be a big breakthrough.
The diesel engine is, by its nature, a dirty beast, but its fuel flexibility, lovely torque, and high MPG keep it an important player in combustion auto engine.
Even if keeping it there requires a constant stream of new cleaning tech.
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