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Influence of Coolant on the Performance of Internal Combustion Engines
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Abstract—The influence of coolant properties on the performance of internal combustion engines is inves
tigated, and means of coolant improvement are considered.
DOI: 10.3103/S1068798X10120129
RUSSIAN ENGINEERING RESEARCH Vol. 30 No. 12 2010
INFLUENCE OF COOLANT ON THE PERFORMANCE 1235
Mg(OH)2, CaSiO3, Ca3(PO4)2, etc. The scale compo
sition depends on the content of various cations and
anions in the water. The rate at which alkalineearth
deposits are formed is largely determined by the heat
flux through the heated layer, since the degree of
vaporization of water is considerably different in the
wall boundary layer. Scale in the cooling system
impairs engine performance, on account of its poor
heat conduction. As a result, even with a small scale
layer, the thermal operating conditions of the engine
components change sharply. With a 1mm scale layer,
the wall temperature of the cylinder is increased by
100–200°C. With 1.5mm scale in the central zone of
the floor and in the upper band of the sleeve, the heat
transfer in the cooling system is reduced by 30%.
The increase in engine temperature due to
impaired heat transfer increases fuel consumption and
reduces engine power. Research shows that, with
(0.5–1.2) mm scale, the engine power is reduce by 7–
13%, while fuel consumption increases by 4–10% [6].
The state of the cooling system considerably influ
ences the wear of the cylinder–piston group. The pres
ence of scale on the cylinder walls is determined by
measuring the volume of the cooling jacket and also on
the basis of the increased oil loss and increased tem
perature due to the cylinder heating associated with
the reduced heat transfer through the cylinder sleeve
and the head of the cylinder block. Increase in the
temperature difference at the outer surface of the
cooling jacket indicates the presence and thickness of
deposits in individual zones of the cooling system.
Modification of the heat conduction of the deposits
permits increase in the motor power by 20% or more
without structural changes in the cooling system.
The chemically aggressive properties and corrosive
action of the coolant may be characterized by the pH
or the electrical conductivity.
At present, corrosive protection of internal com
bustion engines is a high priority [7]. In Russia, the
annual metal losses on account of corrosion amount to
as a much as 12 % of total metal reserves, which corre
sponds to 30% of the metal produced per year. Besides
direct losses, there are indirect losses such as losses of
engine power due to faults and repair time.
The formation of vapor bubbles at the hot surfaces
of the hottest engine components facilitates cavita
tional and erosive failure. The rate of vaporbubble
formation and the heattransfer coefficient depend on
the surface tension and viscosity of the liquid. There
fore, these characteristics may be used to estimate the
operational properties of lowfreezing liquids (aque
ous solutions of ethylene glycol). A deficiency of eth
ylene glycol, which is a component of antifreeze, is its
corrosive action on metal, which is reduced by means
of additives.
For antifreeze, the pH should be no more than 8.5.
Liquids with higher pH produce corrosion of alumi
num and brass components in the cooling system.
Oxidation is also impermissible [8, 9]. Foaming of the
liquid is another problem, since it may be associated
with disruption of the cooling system and liquid leak
age. Therefore, a foam suppressant (such as siloxane)
is added to antifreeze.
In the figure, we present means of improving the
performance of internal combustion engines. Optimi
zation of the physicochemical and thermophysical
properties of the cool increases motor reliability,
improves its economic and environmental character
istics, and reduces the toxicity of the exhaust gases.
The introduction of soluble polymers and surfactants
in the coolant is particularly promising.
The best approach is simultaneous improvement in
the coolants and structural modification of the cooling
system, with the introduction of isolated sections
characterized by variable pressure in hightempera
ture cooling. The heattransfer rate must change in
response to the motor load and speed. To this end, tra
ditional control methods are supplemented by auto
matic regulation of the pressure in the cooling system.
The coolant properties may be changed by various
means, such as preliminary purification, cationization
in ionexchange filters, magnetic treatment, and
ultrasound treatment. Operational experience shows
that the best approach is the introduction of inhibitors
of cavitational and corrosive damage and scale forma
tion, even in small quantities [10, 11].
In terms of composition and effect, coolant addi
tives may be divided into chemical additives and
water–emulsion additives. Chemical additives passi
vate metals by creating protective oxide films on their
surface, facilitate the transfer of scale to the slurry, and
improve the pH.
Water–emulsion additives are anticorrosive oils
formed by dissolving a white stable emulsion in water.
At the cooled surfaces, these additives form an oil film,
Means of improving the performance
Improving Optimization of
Vibration Cavitation
Corrosive
Scale
Heat transfer
Heat
of internal combustion engines
coolingsystem
design
Optimization of
operational parameters
(Tco, Pco, W) coolant properties
and erosive
damage
formation
losses
Mixture
formation
Mechanical
flosses
Means of improving the performance of internal combus
tion engines.
1236
RUSSIAN ENGINEERING RESEARCH Vol. 30 No. 12 2010
ZHUKOV
which prevents corrosion and the formation of depos
its. Moreover, thanks to the damping effect, the oil
film is able to reduce cavitation. This is a definite ben
efit, but water–emulsion additives also have a down
side: the possibility of local overheating on account of
the impaired heat transfer due to the increase in oil
film thickness when the emulsion concentration in the
coolant increases. Accordingly, monitoring of the
emulsion content in the cooling system is essential.
Oilbased additives are able to form a film of thick
ness 0.3–0.5 mm after dieselengine operation for
500–1000 h. On account of the high temperature
(above 170°C) and the catalytic action of the metal
surface, destructive processes develop, with the forma
tion of clogging products and overheating of the
engine [12]. Therefore, manufacturers such as Bur
meister and Wein and Sulzer do not recommend
water–emulsion additives in highpower engines.
We now consider the creation of multifunctional
chemical additives for the basic coolants: water and
aqueous solutions of ethylene glycol.
In selecting the components, the primary consider
ation is their compatibility with the coolants: the
absence of processes such as stratification, foaming,
and residue formation. High efficiency at low concen
trations is also required. (The total content of additive
must be no more than 0.5 wt %.) In addition, they
must be nonflammable, explosionsafe, and nontoxic.
The proposed compositions for water contain
sodium silicate, Sintanol DS10 surfactant, polyacry
lamide, and ammonium molybdate. When using
aqueous solutions of ethylene glycol, the additives
contain polyacrylamide, polyvinyl alcohol, and Sin
tanol DS10. In both cases, small quantities of foam
suppressant are introduced to ensure normal opera
tion of the cooling system.
The additives are subjected to laboratory, bench,
and operational tests in various gasoline and diesel
engines of different power [4].
Gravimetric and potentiostatic methods are used
to investigate cavitation and corrosion. The results
confirm the effective inhibition of cavitation and cor
rosion for the main engine materials: the degree of
protection with water coolant is 90–95% for ferrous
metals and 50–75% for nonferrous metals; for motors
with ethyleneglycol coolant, the corresponding fig
ures are 40–60% and 10–20%.
Surfactants and soluble polymers prevent scale for
mation. The surfactants are adsorbed as a monomo
lecular film on the surface of the newly formed crys
tals, thereby preventing their growth and adhesion at
the surface [13]. The added polymers are present in
solution as micellar structures and prevent the coagu
lation of solid particles over a wide range of solid
phase content. Visual inspection confirms the effective
prevention of scale formation at the heattransfer sur
faces.
Thus, the proposed additives prevent or signifi
cantly reduce the two main problems in liquidbased
cooling systems: cavitation and corrosion; and scale
formation. To investigate the influence of the additives
on the heat transfer, special laboratory equipment is
designed for simulation of heat transfer in the volume
around the coolant sleeve. The equipment includes a
model of the closed cooling system, consisting of the
cylinder sleeve with internal heating, a tank with the
coolant liquid, and a circulation pump. The heater
permits surface temperatures in the cylinder of 180°C
(the temperature at which coking of the oil begins).
The internal heater ensures steady heat fluxes. A ther
mostat in the liquid stores ensures constant initial liq
uid temperature in the system. The circulation rate is
regulated by a system of valves, which produce the
speed range typical of coolant systems in internal
combustion engines (0.1–1.0 m/s), and is measured
by a differential manometer, which is gravimetrically
calibrated for each liquid considered.
Thermometer measurements at the cylinder sleeve
indicate that introducing polyacrylamide in the cool
ant laminarizes the wall layer of liquid and increases its
thermal resistance. This increases the sleeve tempera
ture by 5–10°C in different operating conditions, in
the case of heat transfer without boiling. The introduc
tion of surfactant reduces the surface tension, which
facilitates the formation of vapor bubbles in heat trans
fer with phase transitions and thereby intensifies heat
transfer. As a consequence of these changes in coolant
properties, the temperature of the cylinder sleeve is
reduced by 3–7°C.
By determining the surfacemean heattransfer
coefficient on the basis of the Newton–Richman law,
we confirm the influence of the additives on the heat
transfer. Tests in actual engines permit assessment of
the additives in real operating conditions and show
that the warming of the cylinder assembly by change in
the coolant properties does not lead to motor heating;
however, the heat losses through the cooling system
are reduced. As a result of the reduced losses, the fuel
consumption of the engine is reduced by 2–4% in
nearrated conditions and by 5–8% in intermittent
operation.
The warming of the cylinder sleeve by reduced heat
transfer to the coolant as a result of change in its prop
erties is comparable with the warming on applying
insulating coatings. The change in the thermal condi
tions improves the environmental indices of the motor.
We know that the time τi required for fuel ignition has
a significant influence on the dynamics of fuel com
bustion and the content of pollutants—in particular,
NOx and CnHm [14]. The ignition time τi depends on
the fuel composition and the quality of injection and
also on the air pressure and temperature in the cylin
der at the moment of injection. The temperature and
pressure at the end of the compression cycle depend
on the degree of compression and cooling rate of the
RUSSIAN ENGINEERING RESEARCH Vol. 30 No. 12 2010
INFLUENCE OF COOLANT ON THE PERFORMANCE 1237
cylinders. The degree of compression is determined by
the engine design, while the cylinder cooling rate may
be regulated by various means.
Thermometric data for the cylinder assembly show
that the additives reduce heat transfer through the
cooling system and increase the temperature of the
cylinder sleeve (by 5–10 K on average, depending on
the engine’s operating conditions) [15].
Warming of the cylinders increases the gas tempera
ture within the cylinder on compression. To estimate
the influence of this temperature rise on the ignition
time, we use Wolfer’s empirical formula (obtained from
tests in a calorimetric bomb) τi = 103p–1.19exp(4650/T),
where p and T are the pressure and temperature at the
end of compression, and Semenov’s formula (obtained
in tests of diesel engines) τi = where cp
is the mean piston speed; pin and Tin are, respectively,
the air pressure and temperature in the cylinder at the
onset of fuel injection.
The temperature rise during compression due to
the change in coolant properties reduces τi by as much
as 15%, according to motor calculations on the basis
of the speed characteristic [16]. The greatest effect of
the cylinder warming is observed at small speeds and
loads. This is especially important, since cars spend a
great deal of time in such conditions during urban
driving.
Reducing the fuelignition time slows the pressure
rise on combustion and reduces the pressure and tem
perature at the end of combustion. Therefore, it
reduces toxic emissions, with significant reductions in
the emissions of NOx and aldehydes R=CHO [17].
Because reducing the fuelignition time slows the
pressure rise on combustion, there will be correspond
ing reduction in the noise level.
Calculations show that modifying the thermal state
of the cylinders by changing the coolant properties is a
promising means of reducing the environmental
impact of internal combustion engines, without loss of
fuel economy or reliability.