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Cummins and Scania to Produce Higher Pressure Diesel Injection Systems

Cummins and Scania are working together to produce next-generation fuel systems for heavy-duty on-highway diesel trucks.

The new XPI (Xtra-High Pressure Injection) systems, under development since 2003, will replace the current HPI fuel system, currently produced jointly by the two companies. Production of the XPI systems will begin early in 2006.

Cummins and Scania have partnered on fuel systems development and manufacturing since 1992.

Both manufacturers see the XPI system, which features higher injection pressures together with multistage injection, as an important tool in increasing combustion efficiency. Increased combustion efficiency reduces emissions—and so helping to meet coming EPA 2007 and Euro 5 engine requirements—as well as improving fuel consumption.

Higher injection pressures create smaller fuel droplets and higher injection velocity to promote a more complete burning of the fuel. This, in turn, maximizes power and minimizes pollution. By squirting needed amounts of fuel in a shorter time frame, a high pressure system can accommodate multiple injection events during each combustion cycle—again, allowing the engine control software to optimize combustion for particular conditions.

The XPI systems may reach up to 2,500 bar (that’s some 36,000 psi).



would this cause flocking with biodiesel?


Good question. [Flocking is the term given to the phenomenon of polymerization of biodiesel under high injection pressure, potentially creating little pieces of material that cause clogs in the fuel filter. There have been reports of flocking in some Mercedes and Ford (which uses Cummins diesels) vehicles with high pressure injection systems when burning B100.]

From what I can see, it would depend on the characeristics of the biodiesel and the blend ratio—I’ve only seen references to it with B100 blends, but others may have more detail on the whole issue.

It sounds, though, like there needs to be some good focused research on the topic. And if anyone knows of such, please post.

Older technical paper on Influence of Physical and Chemical Properties of Biodiesel Fuel on Injection, Combustion and Exhaust Emission Characteristics in a DI-CI Engine (2001).


Mike - are you aware of any "point-of-diminishing-returns" with respect to injection pressures in diesel engines? I see that this injection system is capable of 2500 bar.

Will higher and higher injection pressures result in a continuum of increasing performance and decreasing emissions?


I’m sure there are...but I don’t know what they are. :-)

I’ve seen a number of papers on injection pressure, affects on combustion and emissions, etc., but haven’t yet seen one didentifying the “ideal&rdquo. (If any has, please post!)

There are number of factors that go into this, including nozzle design, injection pressure, injection duration, injection profile (single injection or multi injections), resulting droplet size, combustion chamber pressure and temperature.

The transition to HCCI—which appears to be the engine strategy for post- Euro 5 and EPA 2007—will complicate things further with a need for different injection strategies as well.


Obviously the efficiency of the engine is thermodynamically limited. Also, higher injection pressures require more powerful injection systems that consume more power.

So yes, there are dimishing returns. But exactly were they lie I don't know.


With some variations in type and evolution of the injection system, a 1000 bar is the limit where more energy has to be put in than there is advantage in the result of this high pressure. (according to Bosch training centre)


So, i feel the question coming...
Why increase further?

Dazza deisel

There is a new injection system being developed here in Australia, that claims to reduce emissions , saves 30 per cent fuel use and gives 30 per cent more torque than the standard systems. it utilises injection pressures of up to 160,000 psi. yes that is 160,000psi. It is currently being patented, and production should resume in 2 to 4 years.


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