Matt
405
395
18
50
100
150
20
22
24
28
30
0.56
Preliminary analysis has illuminated an important trend: there seems to be an initial "primary" break-in period followed by a longer more subtle "secondary"
break-in period. During the first 5 to 50 hours lubrication oil consumption was very high and emissions were poor, but after this "primary" break-in engine
performance continued to slowly and steadily improve for another 200 to 300 hours at which point it leveled off. This is seen most clearly in Figure 9. (Note that
the first 50 hours are not represented due to lubrication oil measurement and consumption issues.) There is a steady decrease in the lubrication oil consumption
rate until the 300 hour point, at which point consumption rates seem to stabilize. This is likely due to the piston rings still breaking in, which is supported by the
chromium and iron measured in the lubrication oil shown in Figure 10. The chromium and iron content is high initially, while engine parts are still breaking-in,
then a low is reached at 300 hours.
0.54
0.52
0.50
32
18
200
20
22
Injector Timing (ºBTDC)
12
NOx (ppm)
Opacity (%)
4
800
0
600
(b)
32
900
700
24
30
1000
2
22
28
The crank case pressure data also supports this two phase break-in observation. The crank case pressure is an indication of blow-by. As the pressure
decreases, less blow-by is likely occurring. Figure 11 shows a trend almost identical to the lubrication oil consumption. During the first 300 hours a stead
decline is experienced, then at 300 hours the pressure levels out. Figure 12 shows the carbon monoxide emissions and exhaust smoke opacity. Both of these
emissions constituents improve during the first 200 to 300 hours and then level off. These emissions are an indication of the incompleteness of combustion,
lower values indicate better combustion. These results show that at least during the first several hundred hours of operation, when fueled on straight plant oil via
the modification kit, engine endurance issues are not significant. Quite to the contrary - the engine actually experiences a steady improvement in performance
during the first few hundred hours of operation.
70
6
20
26
9 MPa
15 MPa
1100
8
18
Figure 3: (a) Lister Engine Head with Change Over Valve.
(b) COV Plug Preheater Design replaces COV
1200
9 MPa
12 MPa
15 MPa
10
24
Injector Timing (ºBTDC)
(b)
(a)
Figure 2: Plant Oil Viscosity versus Temperature
(a)
26
0.58
26
28
30
32
18
20
Injector Timing (ºBTDC)
22
24
26
28
30
32
Injector Timing (ºBTDC)
60
50
40
30
20
10
0
0
(c)
(d)
Figure 7: Injection Tuning Performance and Emissions. (a) Brake Specific Fuel Consumption. (b) Equivalence Ratio.
(c) Exhaust smoke opacity. (d) Oxides of Nitrogen
100
200
300
400
500
Hour
The equivalence ratio is the actual fuel to air ratio divided by the stoichiometric fuel to air ratio and is a direct indicator of the quality of combustion. Figure 7 (b)
shows the equivalence ratio across the nine test points. In strong agreement with all other engine performance parameters, the equivalence ratio map reinforces
the hypothesis that when fueling the Listeroid CS 6/1 on WVO, optimal tuning occurs at the timing of 25 ºBTDC with an IVOP of 15 MPa.
The engine coolant system was comprised of a 55 gallon drum filled with
water, circulating via a passive thermal siphon cycle. Two type J
thermocouples were used to measure water coolant level entering and
exiting the engine. A thermostat was used in the engine coolant exit to
speed up the rate at which the engine reached steady state (the water
coolant temperature leaving the engine was stable and consistent,
~90C).
The measured opacity values are reported in Figure 7 (c). The results show that at the most advanced injector timing (30 °BTDC), regardless of IVOP, opacity is
worse than at stock timing (20 °BTDC). However, in agreement with the engine performance data increasing the IVOP improves the opacity. This vividly shows
an engine tuning "envelope" effect - advanced timing and increased IVOP improves combustion, but only to a point, where it then begins to hinder combustion.
When injection is advanced too far cylinder conditions are not optimal for good atomization. Temperatures and pressures rise rapidly close to TDC. These
conditions are important for appropriate mixing and vaporization which lead to good combustion. Advancing the injection too much introduces the fuel spray into
cylinder before these conditions are available.
A dual fuel tank approach was utilized – the engine was started on diesel
to allow the preheater to come up to temperature and shutdown on
diesel so that the high pressure fuel lines and pump were purged of the
waste vegetable oil (WVO). Each fuel tank had its own filter. The WVO
was pre-filtered to 1-micron before being added to the fuel tank.
WVO
•WVO under unmodified conditions (room temperature fuel, IVOP of 9
MPa, and injector timing of 20 ºBTDC)
400
200
2
•WVO under modified conditions (fuel heated to 100°C, IVOP of 15 MPa,
and injector timing of 25 ºBTDC).
1
0
30
60
90
Crank Angle
Figure 5: Pre-combustion Chamber Pressure Traces
0.3
Diesel
0.25
WVO
WVO w/mod
0.2
The engine was loaded to 75% and run at 650 RPM. The pressure
transducer was mounted into the COV plug preventing its use as a
preheater, instead the high pressure line was heated electrically.
The pressure traces are shown in Figure 5. Ignition is usually identified
by heat release, specifically the initial spike on the rate of heat release
(RoHR) curve. To accurately calculate the heat release of an IDI engine
both the prechamber and main chamber pressures must be measured.
Though heat release can be calculated with only one or the other
pressure, the calculation can have as large as a 25% error, especially
during early combustion. Due to the availability of only the prechamber
pressure, heat release was not calculated. Instead, ignition was
approximately identified by the rapid change in pressure per change in
crank angle (∆P/∆CA). From Figure 6 ignition can be identified in this
way for each of the three cases. For the purpose of this study the ignition
point was specifically defined as the point where the ∆P/∆CA exceeded
0.15 for 2 crank angle degrees.
0.15
The ignition point and peak pressure point of the diesel and unmodified
WVO cases are nearly identical, though the peak pressure value of the
unmodified WVO case is lower. The modified WVO case showed a
slightly earlier ignition which resulted in an earlier peak pressure point,
and higher peak pressure value. The lower viscosity from preheating,
advanced injector timing and increased IVOP are likely all contributing
factors to this enhancement to the ignition quality.
0.1
0.05
0
-12
-10
-8
-6
7
100
200
300
400
500
-0.360
10
-0.370
8
-0.380
-0.390
Opacity
1200
CO
1000
800
6
600
4
400
-0.400
2
200
-0.410
0
0
0
100
200
300
400
0
500
100
200
Hours
Figure 11: Engine Crank Case Pressure (gauge)
300
Hours
400
500
Figure 12: Exhaust Smoke Opacity
-4
Crank Angle
Figure 6: Change in Pressure per Change in Crank Angle
in the pre-combustion chamber
0.5
before
0.4
100 hours
200 hours
300 hours
400 hours
500 hours
Figure 14: Injector Tip
0.3
0.2
20%
40%
60%
80%
0%
100%
20%
608
60%
408
308
Figure 13: Engine Head
and bottom of valves
after 500 hours
Intake Valve Before
400
8
0
80%
100%
Exhaust Valve After
600
200
60%
Exhaust Valve Before
800
108
40%
Intake Valve After
Figure 15: Valves before and after 500 hour test
Diesel
WVO
WVO w/mod
208
20%
100%
1000
508
0%
80%
1200
Diesel
WVO
WVO w/mod
708
40%
Engine Load (%)
(b)
NOx (ppm)
3
Equivalence Ratio (Φ)
600
808
-30
8
Diesel
WVO
WVO w/mod
Engine Load (%)
(a)
CO (ppm)
Pressure (MPa)
800
0%
4
0
∆P/∆CA
Diesel
WVO
WVO w/mod
1000
• diesel at standard (unmodified) conditions (room temperature fuel,
IVOP of 9 MPa, and injector timing of 20 ºBTDC)
WVO w/mod
0.6
0
A pressure transducer provided by Kulite Semiconductor Products Inc.
was used to map the pressure in the pre-combustion chamber versus
the crank angle. Three cases were tested:
Diesel
-60
9
1200
System BSFC (g/kWH)
The opacity of the exhaust was measured using an AutoLogic model # 3100332 opacity meter to take readings at 16 Hz that were then averaged across a
10 minute sampling window. To measure gaseous emissions, an Enerac 700
integrated emissions system was used to measure O2, CO, CO2, unburned
hydrocarbons (UHCs), NO, NO2, and SO2. Data was collected once per
second as parts per million (ppm) or vol%, depending on the concentration.
Readings were averaged across a ten minute steady state window (steady
state referring to both engine stabilization and the stabilization of the gas
analyzer measurements).
7
-90
10
Figure 4: Experimental Setup
The WVO’s “on-engine” filter (post fuel tank) was 80 mesh, to reduce a
pressure drop that could result in starving the engine of fuel. To minimize
mixing between the two fuels, the injector’s fuel return line was not
routed back to either fuel tank, but instead directly to the juncture of the
two fuel lines (SVO and diesel) situated just before the fuel pump. This
point is labeled as the “fuel cross” in Figure 4.
5
11
The NOx values between the different IVOPs are not dramatically different, as shown in Figure 7 (d). Increasing the IVOP from 9 to 15 MPa does not then
drastically increase NOx. Timing on the other hand does seem to noticeably affect NOx. The envelope is not as sharp, NOx somewhat levels off as timing is
increased past 25° BTDC. NOx formation is commonly attributed to the Zeldovich mechanism (a thermal mechanism). With regard to advanced injection timing
NO formation may increase in two ways. As timing is advanced ignition delay increases but less so than the actual advancement (in terms of crank angle),
resulting in earlier autoignition. Higher NO formation is then related to the longer ignition delay as it allows for more fuel evaporation and mixing in the lean flame
region of the spray. But in other spray regions NO may also increase due to higher temperatures.
The air intake flow rate was measured via an orifice plate & pressure
transducer. A plenum chamber was utilized to attenuate the air flow
pulses, sized per SAE standards. Ambient temperature, pressure, and
relative humidity were measured near the plenum chamber entrance.
6
12
Iron
Chromium
Hours
Figure 10: Lubrication Oil Iron and Chromium Content
Opacity (%)
Figure 7 (a) shows the brake specific fuel consumption for the system (generator and electrical losses were not subtracted). The best performance was found at
the timing of 25 ºBTDC with an IVOP of 15 MPa. These results relate well to the findings of other studies where advanced timing of an IDI engine resulted in
lower BSFC at low engine speeds . The advanced timing aids combustion because the plant oils have longer ignition delay.
Crank Case Pressure (PSI)
A Listeroid CS 6/1, 650 RPM, 4-stroke, 114.3 mm x 139.7 mm
bore/stroke, water cooled, IDI diesel engine was used to drive an ST-5
5kW generator head which was loaded by a bank of light bulbs. The ST5 was chosen to provide the load to the engine because it is a generator
commonly paired with Listeroids throughout the developing world.
Engine load was measured from a power meter which logged volts,
amps, frequency, and power factor. Engine speed was measured with a
Hall Effect sensor and a magnet on the flywheel.
13
0
Figure 9: Lubrication oil Consumption Rate
In order to tune the engine’s timing and IVOP to optimal conditions for the WVO, three timing settings (20 ºBTDC, 25 ºBTDC, and 30 ºBTDC) and three IVOPs (9
MPa, 12 MPa, and 15 MPa) were tested. Higher IVOPs were tested previously but erratic performance precluded further exploration past 15 MPa. Each of these
nine settings was tested three times each at 75% engine load (+/- 1%) and 650 RPM. For all of the 27 tests, the fuel was preheated via the COV plug design
detailed above. The summary of the engine’s performance across these tests is detailed below. Error bars signify standard error across the three repetitions, for
each of the 9 different settings. Figure 7 shows various engine performance parameters. All four parameters point toward an optimized tuning of the injector
timing at 25 ºBTDC with an IVOP of 15 MPa.
100
90
80
70
60
50
40
30
20
10
0
Chromium (ppm)
415
9 MPa
12 MPa
15 MPa
CO (ppm)
425
Temperature (C)
Figure 1: Multi-Function Platform (MFP) in
Rural Mali
0.60
385
0
In addition to the preheater, the modification kit also includes the tuning of
the injector pressure and timing to better atomize given the unique properties
of straight plant oils.
435
Short-run tests (1 to 10 hours in duration) are valuable for understanding the immediate possibilities of straight plant oil fueling, however questions of durability
are left largely unanswered. In order to understand potential endurance issues a 500 hour longevity test was carried out. The engine was run 10 hours a day,
five days a week for 10 weeks, at 75% engine load, 650 RPM. Each day the engine started and stopped on diesel (15 minutes each) to allow the preheater to
come up to temperature and to purge the fuel lines. In between the startup/shutdown the engine was run for 10 hours on WVO (waste vegetable oil). The 500
hour test lasted approximately 10 weeks. At the start and end of the test a detailed physical inspection was made of the engine in which the cylinder bore was
measured and important components were photographed. Every 100 hours during the test the pre-combustion pressure was measured. Every 100 hours
emissions were measured. Every 25 hours lubrication oils samples were taken. Every 10 hours (daily) fuel consumption and lubrication oil consumption was
measured. Several run time parameters were also measured each second, including various temperatures and pressures throughout the engine.
Iron (ppm)
Soybean
Canola
Peanut
Palm
Jatropha
Soy Shortening
Pre-WVO
WVO
Diesel
Candidate in Earth and Environmental Engineering at Columbia University
2Professor of Mechanical Engineering at Columbia University
9 MPa IVOP
12 MPa IVOP
15 MPa IVOP
445
and Vijay
Equivalence Ratio (Φ)
The viscosity of plant oils is much higher then diesel at room temperature,
but as temperature increases viscosity exponentially decreases, as shown in
Figure 2. For this reason a preheater was designed to utilize the unique
COV design of the Listeroid engine, as shown in Figure 3. The preheater is
passive, utilizing waste heat from the engine, making it ideal for a remote,
rural setting.
100
90
80
70
60
50
40
30
20
10
0
System BSFC (g/kWH)
Viscosity (cP)
Though many plant oils have a similar energy density to fossil diesel fuel,
several properties of plant oils are considerably different from those of diesel.
Engine modifications can overcome some of these differences. An engine
modification kit has been designed and tested for a slow speed, stationary,
indirect-injection diesel engine - the Lister-type CS 6/1, common throughout
the developing world. The kit allows vegetable oil fueling with similar
performance to that of diesel fueling. The kit's simple yet robust design is
targeted for use as a development mechanism, allowing remote farmers to
use locally grown plant oils as a diesel substitute, as shown in Figure 1.
2
Modi
Lub. Oil Consump. (mL/Hr)
1Eng.Sc.D.
1
Basinger
0%
20%
40%
60%
Engine Load (%)
Engine Load (%)
(c)
(d)
80%
100%
Bottom
Figure 16: Piston Top
after 500 hours
Figure 17: Cylinder after 500 hours
Figure 8: Multi-Load Performance and Emissions. (a) Brake Specific Fuel Consumption. (b) Equivalence Ratio.
(c) Carbone Monoxide. (d) Oxides of Nitrogen.
From the IVOP-timing maps and pre-combustion traces it was found that an appropriate modification kit would include a COV plug preheater (injector
temperature ~90°C), advanced injection timing (25 ºBTDC), and increased IVOP (15 MPa).
This modification kit was then tested across all engine loads, 10%-90%, and compared to diesel and WVO without the modification kit. The diesel and WVO
were run under stock conditions - no injector preheating, injector timing of 20 ºBTDC, and an IVOP of 9 MPa. Data was taken for each of the three test cases
only after bringing the engine to “steady state” conditions at 650 RPM at each of the five loads tested. Data for each case and for each load was then averaged
across a one hour “steady state” window. These results are detailed in Figure 8.
Generally diesel performed the best, with the modified WVO case performing better then the unmodified case, as shown by the BSFC. The equivalence ratios
for each of the three cases are nearly indistinguishable from one another, though at high loads the unmodified WVO case does have slightly poorer values. At
all loads diesel CO is the lowest. At low loads unmodified WVO is relatively flat, then at mid load the CO begins to increase. The modified WVO case is in
between the diesel and unmodified case. This is likely because the modification improves mixing and evaporation, but the heavier WVO molecules with their
slower evaporation rate still do not burn as completely as the diesel. The NOx values show the diesel to have the highest values across all loads, while both
WVO cases are nearly identical. Like the CO, this points to a more complete combustion in the diesel case, which in turn provides hotter temperatures for
greater thermal NOx generation.
After
Unused
Figure 19: COV plug after 500
hours compared to an unused
COV plug
Top
Figure 18: Main Bearing Shells after 500 hour test
Several critical engine components were photographed before and after the 500 hour test. Figure 13 shows
the bottom of the engine head and valves after the 500 hour test; though there is carbon buildup, it does not
appear excessive. Figure 14 shows the injector tips after each 100 hour period of the test. Every 100 hours
the injectors were pulled and cleaned (when the oil was changed). The photos show significant buildup on
the injector tips, without the 100 hour cleaning fouling and atomization problems may occur. Figure 15 shows
before and after photos of the intake and exhaust valves. The exhaust valve did experience some pitting,
which in time could cause seating and sealing problems. Figure 16 shows the piston top after the test. There
is carbon buildup but it was surprisingly small. Figure 17 shows a top portion of the cylinder from a side view.
This wear is surprisingly noticeable, the rest of the cylinder appeared in good shape but this top portion,
where the intensity of compression and combustion takes place, experienced significant wear, scratching and
carbon buildup. Figure 18 shows the main bearing shells (the lubrication oil was wiped off for the photo).
There was surprisingly little wear, no major scratching, only minor scuffing. Figure 19 shows the COV plug
after the 500 hour test compared to an unused COV plug. There is a large amount of carbon buildup on the
COV plug. This portion of the COV plug sits inside the pre-combustion chamber near the injector tip. This
may point to the need to remove and clean the COV plug regularly, similarly to the cleaning regiment for the
injector tip.