05-02-2013, 11:21 AM
Use of Vegetable Oil Lubricant in a Low Heat Rejection Engine to
Reduce Particulate Emissions
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ABSTRACT
Thermal barrier coated diesel engines, also known as
low heat rejection (LHR) engines, have offered the promise
of reducing heat rejection to the engine coolant and
thereby increasing overall thermal efficiency. However,
the larger market potential for thermal barrier coated
engines may be in retrofitting in-service diesel engines to
reduce particulate emissions. Prior work by the authors
has demonstrated a significant decrease in particulate
emissions from a thermal barrier coated, single-cylinder,
indirect injection (IDI) diesel engine, primarily through
reduction of the volatile (VOF) and soluble (SOF) fraction
of the particulate. This prior work relied on conventional,
commercially available, petroleum-based lubricants. The
present study concerns the additional benefits for particulate
reduction provided by vegetable oil lubricants.
These lubricants are derived from renewable resource
materials and can provide a reduction in lubricant generated
particulate matter.
INTRODUCTION
The major promises of thermal barrier coated (also
known as low heat rejection, LHR) engines were
increased thermal efficiency and elimination of the cooling
system [1]. A simple first law of thermodynamics
analysis of the energy conversion process within a diesel
engine would indicate that if heat rejection to the coolant
was eliminated, the thermal efficiency of the engine could
be increased. However, due to a number of challenges
posed by the presence of thermal barrier coatings within
the engine, these particular promises have not been kept.
EXPERIMENTAL
APPARATUS AND TESTING PROCEDURE – A schematic
of the engine test cell is shown in Fig. 1 and specifications
of this engine are listed in Table 1. As seen in
the figure, the engine was coupled to a Clayton waterbrake
dynamometer. The dynamometer torque was
measured using a strain gauge load cell and the speed
was monitored using a 60-tooth gear assembly. The
exhaust, lube oil and coolant temperatures were also
measured to monitor engine operation. The temperature
of the exhaust gas was monitored with a type-K thermocouple
mounted in the exhaust manifold. The data acquisition
system was a Gateway 2000 P-5/100 MHz
computer with a DAS-8/PGA data acquisition and control
board from Keithley Metrabyte. The computer was set up
to log real-time engine speed, torque, power, and temperatures
of the exhaust, lube oil and coolant.
RESULTS AND DISCUSSION
Because vegetable oils typically exhibit lower volatility
than petroleum-based lubricants, one may expect that
vegetable oil lubricants would be ideal candidates for use
in low heat rejection and uncooled (so-called adiabatic)
engines. One would expect to see increased lubricant
consumption in a low heat rejection due to the higher incylinder
temperatures that arise from the thermal insulation
of the cylinder. A lower volatility lubricant would lead
to lower lubricant consumption and could counteract the
tendency for increased lubricant consumption in a low
heat rejection engine. With an uncooled or insulated
liner, the increase in cylinder liner temperature near TDC
at full load can be 100°C or higher. Higher liner temperatures
frequently result in lubrication problems due to
increased oil consumption and lower volumetric efficiency
caused by heat transfer to the intake air. For this
reason, it is generally preferred to leave the liner cooled
and uninsulated. Alkidas [16] found a significant increase
in the volatile fraction of the particulates emitted by an
uncooled engine with an air-gap insulated piston, firedeck,
and exhaust ports.
CONCLUSION
A vegetable oil lubricant based on sunflower oil was
examined in a baseline and a ceramic-coated engine to
determine whether the vegetable oil lubricant would
reduce particulate mass emissions due to the lower volatility
demonstrated by some vegetable oils. The results
show that when compared with a standard SAE 10W-30
commercial lubricant, the high oleic sunflower oil results
in lower total particulate emissions in the ceramic-coated
engine configuration. Under low load conditions, particulate
emissions were lower for the baseline engine configuration
with the vegetable oil lubricant. Specific fuel
consumption was higher for the ceramic-coated engine
configuration than for the baseline engine configuration,
and was somewhat higher for operation with the vegetable
oil lubricant. Lubricant consumption was lower for the
vegetable oil, but lubricant consumption was only monitored
qualitatively.