exsimguy1 wrote:There is (2004) some good research comparing compressibility of different fuels and their changing of firing points related to static timing settings in Bosch inline pumps found here.
Um . . . yes & no. At injection pressures (let's say, over 1500 PSI), there is some measurable difference in the compressibility of various diesel fuels.
However, we are not talking about varying the output pressure of the IP, only the output volume, and the feed pressure range is something around zero to something above, say, 30 PSI. Fuel in the IP housing is in that range (excepting the plungers area high sides and on out). Perhaps even a bit below zero in a plugged-filter circumstance.
In that range of pressures, diesel fuel's density does not change (to any appreciable degree; we are talking really,
really hard to measure differences now).
Not much but one paragraph, unless you register, but it's a good paragraph nonetheless.
This 2003 abstract is fun, lots of colored lines and terse summaries.
One of the two listed test engines they used (the other being a Yanmar DI One cylinder air-cooled) is a Cummins 5.9 ISB, which
seems (five minutes Googling did not yield a definitive answer) to have been available with at least three low-pressure IPs: A Bosch VE, a pretty much similar-to-SD inline IP, and a Bosch VP44. After that, they went common-rail. I probably have part of that wrong, but in any event at least the common-rail (HEUI) and the VE will not be applicable to any discussion of IP housing pressurization effects as relevant to the SD IP.
I noticed some overlap in the staff of both publications, so it would be fair to say that pretty much the same people came to pretty much the same conclusions in 2003/2004. Interesting stuff. What Andre & Rick say is that they've measured the static & effective timing changes when mechanical factors are held constant but the fuel composition is changed. Vegetable oil and various blends of biodiesel and other fuels (LSD, ULSD, COP FT) show differences in static and effective timing (and peak cylinder pressures, brake-specific fuel consumption, NOx, output to later diesel particulate filtration systems).
A fair summary would be to say that BD does not compress as much as D2, at common injection pressures, and that this "stiffer" liquid column allows the action of a IP high-pressure plunger to be transmitted to the injector in less time.
The left chart on page 6 is filch-worthy:
About 1.5° advance is what is indicated. That's just the
mechanical difference in the fuels: independent of cetane/ignitability factors. Which is a number I'd heard before from other sources, so I'm not surprised, and it ties in neatly with Philip's cackling too
![Wink ;)](./images/smilies/icon_wink.gif)
Oops, I meant Philip's cacking problem . . . um, the cold cackling of Philip's SD. There.
(I want to take this opportunity to say, "kilo-joules per degree". That's not a phrase I see on the legend of a graph very often!)
None of which seems to relate to IP housing feed pressure affecting injection timing.