Cummins/Tula dDSF (diesel Dynamic Skip Fire)

[ShinerBock]

I have been watching this study for a while along with the Cummins ETREE project that replaced an ISB 6.7L with an ISB 4.5L hooked up to a 130kW generator pushing a 175kW motor that netted over 60% better fuel economy without any sacrifices to performance. The dDSF project was a partnership with Tula Technology which basically uses special algorithms in the ECM to skip injector firing events based on different loads.

It is sort of like variable displacement systems in gas engines, but more dynamic since it uses an array of different firing densities(up to 30) versus just 8 to 4 cylinder deactivation. The firing density will depend on torque demand. This study was done on a class 8 truck that is rarely unloaded like our pickups so the instances of low torque demand would be more frequent in our trucks and could possibly increase fuel economy, even more, when unloaded.

The best part is that not only does it not add more mechanical complexity (other than an ECM that can handle more data at a faster rate), but it also lowers emissions so current EGR/SCR systems will not be used as much while increasing fuel economy by about 20%(in a class 8 truck). I was told by some of my contacts at Cummins that this will likely be implemented into the larger medium/heavy-duty engines first and then the light-duty commercial market shortly thereafter. It would be interesting to see it work if it is eventually implemented in our pickups.

A 20% increase on the average combined fuel economy of 15.5 mpg in the current Cummins diesel pickups is an additional 3 mpg.

Cummins and Tula study of Diesel Dynamic Skip Fire

[BenK]

RoyJ....ditto...that chart is almost exactly what PWM looks like from experience in Industrial Motor Controls

Add that today's computer systems & injector systems are fast enough to keep the combustion chamber at the diesel stoichiometric air-fuel ratio 14.5:1 and even leaner in other parts of the CC

Am guessing so much leaner to get as complete a burn as can...that NoX might become an even higher issue(s)

RoyJ wrote:
Both real exciting technologies in the diesel front. The Skip Fire is almost like PWM for electric motors, and may be the big step we're waiting for in in-cylinder emissions control vs relying solely on after-treatment. Hopefully 1 day we can look back at the past 15 years as a "interim" emissions phase, much like gas engines of the 70s and 80s.

I've been saying for years we should look at series hybrids used on trains (GE's AC-AC drives can hit 90+% efficiency). It's much easier to optimize your prime mover for a few set-points, than a 3-D map of rpm vs throttle position.

With a battery, we can't use pure AC-AC of course. But a battery is also necessary because unlike a locomotive, we need more than 8 throttle settings, and also need instant response. The extra reserve capacity of the battery should make up for the rectification / inversion losses of AC-DC-AC.

[stsmark]

It’s very similar to the Hyllion ERX. They’re using CNG for the generator fuel. Dana is their partner on the drive axle/ motor.

[ShinerBock]

Groover wrote:

ShinerBock wrote:

Groover wrote:

If the 4.5l engine is expected to do the work of a 6.7l it will be interesting to read what they did to ensure long life.

The 4.5L is pushing a 175kW(234 mechanical horsepower) electric motor in a hybrid setup so it is not primarily the diesel engine that is doing the work. Very similar to a diesel-electric train setup.

But all of the power still originates with the diesel engine unless there is a plug in battery pack that I am missing.

Yes, there is a battery. It is in the technical drawings in the link that I posted.

[Groover]

ShinerBock wrote:

Groover wrote:

If the 4.5l engine is expected to do the work of a 6.7l it will be interesting to read what they did to ensure long life.

The 4.5L is pushing a 175kW(234 mechanical horsepower) electric motor in a hybrid setup so it is not primarily the diesel engine that is doing the work. Very similar to a diesel-electric train setup.

But all of the power still originates with the diesel engine unless there is a plug in battery pack that I am missing.

[garyp4951]

Maybe power your house too when it goes out:)

[spoon059]

I don't understand the majority of what you wrote, but I like the idea of a smaller engine, similar power and better fuel economy.

[RoyJ]

Both real exciting technologies in the diesel front. The Skip Fire is almost like PWM for electric motors, and may be the big step we're waiting for in in-cylinder emissions control vs relying solely on after-treatment. Hopefully 1 day we can look back at the past 15 years as a "interim" emissions phase, much like gas engines of the 70s and 80s.

I've been saying for years we should look at series hybrids used on trains (GE's AC-AC drives can hit 90+% efficiency). It's much easier to optimize your prime mover for a few set-points, than a 3-D map of rpm vs throttle position.

With a battery, we can't use pure AC-AC of course. But a battery is also necessary because unlike a locomotive, we need more than 8 throttle settings, and also need instant response. The extra reserve capacity of the battery should make up for the rectification / inversion losses of AC-DC-AC.

[ShinerBock]

Groover wrote:

If the 4.5l engine is expected to do the work of a 6.7l it will be interesting to read what they did to ensure long life.

The 4.5L is pushing a 175kW(234 mechanical horsepower) electric motor in a hybrid setup so it is not primarily the diesel engine that is doing the work. Very similar to a diesel-electric train setup.

[Groover]

"Diesel engines already emit less Co2 than an equivalent gas engine"

Regardless of the fuel there should be a strong correlation between fuel consumption(or savings) and CO2 output. Those statements may have come from different trucks too.

If the 4.5l engine is expected to do the work of a 6.7l it will be interesting to read what they did to ensure long life.

[ShinerBock]

Groover wrote:
A 4.5l in a class 8?! Or have mixed in information from different tests? Either way, I like the concept for a motorhome if the 4.5l can be made quiet enough to be acceptable for use a generator in a campground. Having separate engines for propulsion and generator in a motorhome complicates a lot of things and adds a lot of weight.

I spoke with a high level person at Thor recently and he told me that there was something like this in the works.

The article doesn't mention use a hybrid but could add a lot to the versatility of the drivetrain.

I don't understand how they increased fuel economy 20% but only reduced CO2 emissions 5% though.

The ISB 4.5L was in a class 6 cab-over truck. You can find more info on that study here.

Cummins ETREE Final Report

Diesel engines already emit less Co2 than an equivalent gas engine even without emissions equipment so I doubt you will see much improvement there. It is NOx that they emit more of and cannot be reduced with a catalytic converter like a gas engine due to a diesel's lean air/fuel ratios. It would ruin a catalytic converter very quickly.

[Groover]

A 4.5l in a class 8?! Or have mixed in information from different tests? Either way, I like the concept for a motorhome if the 4.5l can be made quiet enough to be acceptable for use a generator in a campground. Having separate engines for propulsion and generator in a motorhome complicates a lot of things and adds a lot of weight.

I spoke with a high level person at Thor recently and he told me that there was something like this in the works.

The article doesn't mention use a hybrid but could add a lot to the versatility of the drivetrain.

I don't understand how they increased fuel economy 20% but only reduced CO2 emissions 5% though.

[BurbMan]

Definitely cool tech! Fuel injection in gas engines has been doing this for 20 years, where the the PCM varies injector pulse width based on power required. Longer injector open time = more fuel delivered into the cylinder. The fuel pump operates at a constant flow, and whatever fuel isn't used by the engine gets returned to the tank via the return line. Now some mfrs are using variable-speed fuel pumps to eliminate the return line to the tank.

Hopefully this technology in a diesel application will deliver good emissions performance without the EGR and other problematic components.