Oilseeds for Fuel, Feed and the Future
University of Montana -
Abstract: A Kubota tractor in operation at the PEAS
Farm in Missoula, MT was retrofitted with an Elsbett single-tank system to run on
straight vegetable oil (SVO). A second tractor was run on 20% biodiesel -- and
a third tractor used petroleum diesel as a control to analyze the differences
of each fuel in farming operations.
1) What did you hope to accomplish?
The primary focus of this study is to analyze the
feasibility of running a Kubota tractor with straight vegetable oil as a fuel
source. If we can conclusively determine that vegetable oil is a viable fuel
for a small-farm tractor in Montana, we will then be able to move towards our
vision of growing and utilizing an oil seed crop to keep energy demands of the
2) What did you do?
The initial scope of our study was to comparatively
analyze three similar Kubota tractors running on different fuels. The two
tractors running on a biodiesel blend and straight petroleum did not exhibit
any operational problems during the 2007 farm season. The primary focus of the
study focused on the retro-fit and performance of the tractor running on
straight vegetable oil. Details of the retro-fit process include the following
Research to choose the Elsbett:
For those wishing to maximize the use of SVO, whether for
economic or environmental benefits, an appropriate vegetable oil system must be
used to preheat the oil and facilitate efficient combustion of the fuel.
Because the PEAS farm tractor is typically operated for shorter durations,
research into alternatives yielded a single tank system manufactured by Elsbett
of Germany. These systems are designed to run on SVO solely, and engine
modifications take into account the difference in fuel properties of SVO.
German Elsbett system conversion:
The general modifications of the single tank system are:
- Modification of the fuel cycle to facilitate warming the SVO: this
involves both an engine-coolant heat exchanger in-line from the fuel tank, and
a fuel filter equipped with a 160W heating band.
- Modification of the factory injectors using new injector nozzles
that optimize the spray pattern best suited for SVO.
- Modification of the glow plugs to allow longer cycling period for
extended heating of fuel-air charge.
- Replacement of stock rubber fuel lines with biofuels-resistant
fluoroelastomer (Viton©) hose.
Test tractor: 2006 Kubota L4630 model with indirect
injection, vertical, liquid cooled 4 cycle diesel. 4 cylinder, 2197cc
displacement, 47.2 hp (35.2kW) gross, 44.7 hp (33.5 kW) net at 2700 rpm.
SVO conversion kit: Elsbett kit for Kubota 03-M-series-V2203M/-//2197ccm/36.4kW/49.5PS/BHP/2800rpm part#70000250
Oil: SVO used is crude Morlin linoleic safflower from Culbertson, MT.
Figures 1 and 2 illustrate the stock Kubota and converted
fuel systems, respectively. Discussion follows.
Specific modifications of the fuel cycle are:
1) Routing the fuel pump upstream of the filters, presumably
to supply the needed pressure to effect filtration.
2) A 'T' immediately downstream from the pump regulates flow
of fuel to either the Elsbett filter only (normal operation) or through both
the Elsbett and the Kubota filters (heavy loading only*).
3) The Elsbett filter is equipped with a 160 watt heating
band whose operation is governed by an engine coolant temperature sending
switch (the band is in heating mode only until normal engine operating
temperatures are reached).
4) Downstream from the Elsbett filter is a heat exchanger
with unregulated flow of engine coolant.
5) Injector nozzles supplied with the kit replace the stock
*Under heaviest loading in the dyno test, opening and
closing this valve had no effect on power, indicating that there was sufficient
fuel flow through the single Elsbett filter.
Specific modifications to the glow plug circuit are:
1) Special (heavier duty) glow plugs are supplied, along
with necessary wiring, relays and fuses. Figure 3 illustrates the relationship
to the relevant parts (note: this is not a complete wiring diagram)
The basic operation is: On cold start-up, the coolant
temperature switch is closed, and power flows to both the filter heating band
and the glow plugs, so all fuel warming results from these two systems (coolant
flowing through heat exchanger is cold). Once engine is started, filter heating
band remains on, and glow plugs continue to cycle. Once the engine(and coolant)
reach operating temperature, coolant temp switch opens, shutting off power to
both filter heating band and glow plugs. Thereafter, all fuel heating comes
from the heat exchanger and any radiant heating from the engine block.
The engine conversion was performed as per kit instructions
with one deviation: the kit supplied glow plugs were 2.5 mm longer than factory
glow plugs. The Kubota dealer expressed reservations about clearance between
the tip of the new glow plugs and the bottom of the combustion pre-chamber, and
that installation might result in damage to the interior of the engine. During
conversion, tests made on the length of kit glow plugs were inconclusive; we
measured the resistance of both sets of glow plugs at 0.9Ω, and erring on
the safe side, re-installed the factory plugs.
3) What were the results this year?
The tractor was utilized for normal farm operations over the
course of the 2007 agricultural season at the PEAS farm. The tractor was
regularly monitored and tested over the course of the 2007 season to measure
and record changes in tractor performance.
The tractors running on B-20 and petro-diesel did not
exhibit any observed or measurable problems. However, the tractor running on
SVO did exhibit performance-related problems which we are investigating as a
part of this study.
Initial Results: April 2007
Initial cold-start was rapid (2-3 sec); the engine ran
smoothly, but exhibited an erratic idle which cycled between 1000 and 2000 rpm
over a 1-2 sec. period. After ~10-15 sec., the idle settled down and the
tractor operated normally. The exhaust has the burned-fryer oil smell
characteristic of diesels run on biofuels.
After two months, some staff
reported hard cold starting, even when night temperatures remained around 60°F
and daytime temperatures were 90°F+. Inspection of the glow plugs revealed
moderate-to-severe burning of the tip and loss of continuity between electrical
connection and the glow plug tip, indicating failure.
Loss in horsepower:
Results of dynamometer testing
performed before and immediately after the conversion, and then three months
later, are illustrated in figure 4. The drop in horsepower after conversion is
typical of the decrease in power due to the energy density of SVO
(approximately 9% lower than #2 diesel). However the ongoing decline in hp from
the second to the third dyno test is of concern and will be monitored on an
Dyno testing results:
4) Were there any unanticipated results or surprises you encountered along the way?
After experiencing hard starting in the middle of the summer
(July 6th), we had to determine what was responsible for the
starting difficulties. After pulling out the glow plugs, we noticed an
excessive amount of plug deterioration and asymmetric carbon buildup indicating
engine combustion problems (figure 5).
Straight Vegetable Oil Chemistry:
The current hypothesis is that the tractor starting problems
are due to the chemistry of the vegetable oil we are using in the tractor. The
vegetable oil we have been using was chosen due to its low viscosity, which was
thought to be the foremost issue to overcome any problems using veggie oil in a
The current molecular formula is a triglyceride molecule
that contains multiple Carbon double bonds (Figure 6). A molecule with multiple
Carbon double bonds tends to be more reactive under heated conditions than a
molecule containing fewer or no double bonds. We believe that this chemical
structure is reacting too early in the pre-combustion chamber causing a Carbon
build up or polymerization in the engine. This Carbon build-up is illustrated
by the left glow plug in figure 5 and is consistent with our subsequent engine
analysis (Appendix A).
Figure 6: A triglyceride with multiple Carbon double bonds
We will be using a vegetable oil blend that contains fewer
double Carbon bonds this upcoming season as a means to overcome the presumed
reactivity problems in the 2007 agricultural season (Figure 7).
Figure 7: Relationship comparing viscosity and reactivity to Carbon double bonds
5) Were there any particular practical or policy barriers
you encountered as you conducted this project?
Communications with the Elsbett Company has been a major
challenge. Instructions were in broken English and did not adequately provide
enough detail for the conversion. Several minor pieces of the kit were either
missing or did not properly fit our tractor. The company did not answer their
customer service phone line and did not respond to questions via e-mail.
Fortunately, we were able to rely on recommendations from the Missoula Kubota
dealer, but even this was burdensome for us and them.
It may be worthwhile to identify and survey other people who
have purchased and installed an Elsbett single-tank modification. The Elbett
system appears to be a burgeoning product for the use of biofuels and one would
presume they would have a reliable customer service department.
6) How will you use what you have learned?
Future of SVO Project at the PEAS Farm:
The tractor engine will be broken down and analyzed to
determine the cause of tractor starting problems and decreased horsepower
(Appendix A). If fuel-type is deemed suspect, we will continue research to
determine the most appropriate type of fuel for use with the single-tank Elsbett
The start of the next agricultural season is very near so we
are hoping to make the tractor available to the farm as soon as possible. This
season we will focus on the performance of this tractor exclusively since we
did not notice any changes in the other two tractors last season.
When we reach a point of measurable accomplishment in this
study we would like to distribute our findings to those interested in the
potential for using vegetable oil as an alternative to petroleum diesel.
On 2/21/07, we started up the tractor and drove it into a
garage for inspection. The diesel mechanics from the COT were present and
commented that the tractor ran and sounded normal. Inside the garage, we
removed the injectors from the tractor and a significant amount of carbon was
found plugging up the precombustion chambers. The glow plugs were removed and
exhibited an excessive amount of wear. When removing the #4 injector, the
precombustion chamber was missing. We are assuming that the precombustion
chamber must have burned hot enough to deteriorate and get passed into the
engine and out the exhaust. This was not expected considering how well the
tractor ran just an hour before. Further inspection and work on the engine is
The engine will be dismantled to determine how extensive the
damage is. The injectors will be rebuilt and the glow plugs replaced. Until we
see the condition of the engine, we can only hope there is no cylinder or head
University of Montana: Environmental Studies Program ~ PEAS Farm
Josh Slotnick: firstname.lastname@example.org ~ EVST Faculty/PEAS Program Director
Steve Nelson: email@example.com ~ Technical/Chemistry Consultant
Derek Kanwischer: firstname.lastname@example.org ~ EVST Graduate Studies
Ruston Mitchell: email@example.com ~ EVST/Chemistry Studies