[PunchyHamster]

They have no driving electronics, electronic throttle, ECU controlled injection etc, so you are limited, you can't for example easily make it go constant set speed, because the throttle isn't electronic.

It went a bit too far, optimum would be modern enough to have drive by wire but with open ECU and documentation

[dghlsakjg]

You can still control a completely mechanical engine to work with set speeds. There are mechanical governors that can do this, or you can get an electronic component that moves the throttle for you. Fixed speed engines with variable load are much older than the transistor.

It is no harder than doing it with an ECU, except that you need to install a servo or speed governor with hand tools, instead of fiddling with ECU code.

[PunchyHamster]

It is far easier for 3rd party stuff to target say open bus protocol rather than a servo + speed sensor pair.

[dghlsakjg]

From a software perspective it’s the same. The software doesn’t care if it is telling a servo to rotate or an ECU to increase speed. Both systems need an external speed sensor feeding in. The only extra on the mechanical engine is adding a generic servo.

Both systems can use an open bus protocol. The mechanical system resists proprietary rent seeking as an added bonus.

We’re commenting on an article about farmers willing to pay for tractors with rebuilt all mechanical engines when the exact same tractor could be built with a new computer controlled one. That choice was intentional.

[jcgrillo]

It has a governor.. The P pump 12 valves (and many other multi-application diesels) come with either one of two different governors, an automotive one which has a high idle and low idle, but unrestricted fueling in between. This is what you want in a car or truck where you're controlling road speed with your foot. There's also the "industrial" governor that essentially maps lever input linearly to engine RPM, and endeavors to maintain its set RPM independent of load. This is the kind you find in tractors, generators, boats, etc.

These governors are basically mechanical analog computers which use the inertia of flyweights, springs, and some very clever linkages to do their thing.

[PunchyHamster]

I know, I used tractor like this. Governor only keeps RPM, not the air-fuel ratio and a bunch of other emission and fuel usage related stuff.

And it's a bit easier to make 3rd party addons when you just have some open bus standard, not "mount that servo on a gas pedal"

[jcgrillo]

There's a device called an "aneroid compensator" that sits on top of the governor and is used to maintain a fueling profile for a specific density altitude (e.g. limit fuel at higher altitudes on naturally aspirated engines or off-boost on turbocharged engines). This effectively maintains AFR, although it is not a closed loop system. For closed loop control you need to measure AFR directly in the exhaust and compensate, which means you need (at least, a common rail system that can time injection events independently from the valve train would be even better) an electronically governed injection pump. There's no good way to do this with some 3rd party add-on. You'd be much better off just using an electronically governed Bosch injection pump (like those found on 24 valve Cummins or 1998-1999 Mercedes OM606 turbodiesels). But then you incur the encumbrance of the ECU and all the bad corporate behavior that comes along for the ride.

Also note that maintaining a particular AFR in a diesel is kind of a non goal, at least from the perspective of engine performance. With the older style, simple injection systems that are user serviceable you only get one pulse per cycle. So you can't really change AFR without compromising torque output. For a tractor, when I set the lever all the way forward I (the operator) expect it to maintain revs sufficient to maintain 540rpm at the PTO unless it is not able to do so (fueling maxed out under load). Putting more load necessarily means more fuel in for a given RPM, ergo higher AFR. Note that turbocharging changes this equation a little.