With the DD 16 and the DD 13, there are two Gen 5 engines available from Detroit in the Western Star X Series. The Gen 5 is the new classification for the latest Detroit and is used to differentiate between the progress of the various iterations of the DD13.
Gen 1 was the original version of the 13 litre, Gen 2 saw it change to meet US EPA 10 emission rules by using adblue, Gen 3 never got into Australia, Gen 4 is the engine that’s in the Cascadia in Australia.
This new Gen 5 is now in production, with similar emissions to Gen 4 but with improved fuel economy. There’s quite a few internal differences in this new engine including compression ratio, the shape of the pistons, the way fuel and air flow inside the engine happens with an improved swirl motion.
The main significant difference is in the after-treatment system. The SCR system is in a box which is physically smaller, but has a larger DPF inside, with improved surface area, from a single DPF instead of two smaller ones. This enhances two elements, it reduces back pressure, reducing fuel consumption and secondly it also substantially increases the time between regeneration events.
Regeneration parameters on the original DD13 started after 20 hours, but on both DD16 and DD13 Gen 5 this has pushed out to 125 hours. In fact, on the DD13, in particular, and to a certain extent on the DD16, if the service cycle is anything other than a high idle time application, it manages the temperature well enough to get close to a position where it never needs a regeneration.
In addition, if an operation does have periods where the engine does have to idle for long periods, they can choose an option which auto elevates rpm when required. The engine senses the exhaust temperature is getting a bit low, in a high idle time application, and it pushes the idle speed up to about 1000rpm.
There is also thermo coasting, which is essentially the system going to engine brake on three cylinders, and fuel on the other three. It powers itself against the engine brake, which puts quite a lot of heat through the exhaust. There’s no net change in torque and the system only activates when the truck is in cruise control.
Detroit reckon the driver doesn’t notice any difference, other than the engine sounding a bit odd. The driver can be just cruising along at 100km/h and sees a green light illuminate, on the dash. The whole process can take around 20 minutes on the road.
According to Detroit, by retaining EGR, good fuel consumption gains have been retained. The engine was always designed to have EGR and has, historically, had a low failure rate on EGR valves, coolers, piping or turbochargers.
Depending on the duty cycle the truck is working in, the system will choose its own mix of emission control. It can use all EGR or all SCR, or a mixture of both, depending on the load and any other parameters which might effect the exhaust gases. The data from engine management, NOx sensors, torque needed enables the engine management to calculate its requirements and the solution which suits it best.
By using this mix and match process the engine can run hotter, with higher combustion temperatures burning fuel more efficiently. These higher temperatures do mean higher NOx in the exhaust but fuel efficiency is improved and the SCR can handle the NOx.
The DD13 and DD16 engines now being used in Australia are the same as those used in North America and no longer a specific engine for Australia. The DD16 still has turbo-compounding included in the system, where an air turbine is connected to a gear train that feeds power back onto the flywheel.
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