Just curious, I heard a brief discussion on a radio program, said modern diesel engine designs are fundamentally different than past designs, having to do with the fuel injection system apparently, w/modern diesels being more like gasoline engines now. I can’t think of any big differences, other than the fuel-specs have changed, the old designs were direct injection, and the new designs are presumably the same. What differences are they talking about?
Early diesels were mechanically direct injected with mechanical pumps acting like big distributors. Some were supercharged, some turbocharged. Some were 2 stroke diesels.
Modern diesels use electronic direct injection (like many modern gas engines) controlled by an ECU and are 4-stroke designs. Very easy to adjust injection timing, double-hit the injector (2 or more squirts) to improve power and reduce emissions. 4 valve designs (like gas engines). Many with EGR and exhaust post-treatment. Most modern diesels engines are turbocharged because diesels love to run lean and love pressure.
3 Likes
Older diesel engine fuel systems were pump and lines or unit injected. Unit injected means the injector supplies the injection pressure, usuallly 4-5000 psi. Modern diesel engines are common rail, in which high pressure fuel (30000+ psi) is supplied to electronically controlled injection nozzles. The electronics controls the injection timing and fuel delivery for cleaner burning and less Nox.
1 Like
The fancy exhaust treatments (diesel exhaust fluid and the regenerating diesel particulate filters) are pretty big changes as well.
Ok, I think I’m finally getting the picture. Older diesel designs, the injectors were similar to VW’s CIS gasoline injectors. Those injectors are always “on”; i.e. they’ll immediately inject whatever is delivered to their input. The injector’s job for the older system was primarily to deliver the correct spray pattern.
Newer diesel designs, the injectors have an electric solenoid valve, and are programmed by the drivetrain computer to either be on or off. The % of time they are on sets the fuel delivery rate.
It seems like one challenge for the newer design is containing the pressure needed in the fuel rail, since it has to be held there under very high pressure. Fuel rail leaks might be more of a problem with the newer design.
1 Like