Bulletin of the Transilvania University of Braov Vol. 7 (56) No.

2 - 2014
Series I: Engineering Sciences

IMPROVING DIESEL ENGINE

PERFORMANCE BY AIR-TO-AIR
INTERCOOLING

Veneia SANDU1

Abstract: The paper studies the increase of performance of a heavy duty

turbocharged diesel engine when the intake air is cooled in an air-to-air heat
exchanger, being turned into a turbocharged and intercooled engine. There
were presented dynamometric tests, being evaluated engine performance
parameters such as rated power, torque, hourly and specific consumptions
and smoke level on the speed characteristic at total load. A stress is laid on
the influence of air charge thermodynamic parameters on cooler
effectiveness and pressure loss.

Key words: diesel engine, intercooling, air-to-air cooler.

1. Introduction lower NOx emissions [1-3].

The most practical solution for air charge
The engine manufacturers are always in cooling is the use of an air-to-air heat
search of methods to increase the power exchanger, which is typically placed in
output at the same volume displacement. front of the coolant heat exchanger in
By applying the thermodynamic laws, the vehicle configurations.
quantity of air - fuel mixture inserted in The effectiveness of the air-to-air heat
combustion chamber can be raised exchanger () is defined as the ratio of the
primarily by turbocharging, which leads to real charge air temperature drop across the
the increase of air pressure and cooler core to the temperature differential
temperature in the combustion chamber available for cooling [1]:
meaning that engine operates at a higher
thermal load. Secondly, the charge air can T2 T3
be cooled allowing higher mass of air to be , (1)
T2 T1
introduced in the combustion chamber,
every cycle, thus leading to higher power
output and lower fuel consumption. Also, where: - heat exchanger effectiveness;
the charge air cooling reduces the T1 - temperature of the ambient cooling air;
temperature in cylinders and exhaust T2 - temperature of charge air entering the
system, improving engine durability. On cooler (approximately equal to compressor
emissions, intercooling produces lower discharge temperature); T3 - temperature of
smoke (particulate) emissions as effect of charge air exiting the cooler (approximately
higher density and air-fuel ratio, as well as equal to intake manifold temperature).

1
Dept. of Mechanical Engineering, Transilvania University of Braov.
20 Bulletin of the Transilvania University of Braov Series I Vol. 7 (56) No. 2 - 2014

The air flow through the cooler induces as well as pressure sensors to measure oil
pressure loss which can be calculated using and air charge pressure.
Equation:
Engine technical data Table 1
p pu p d , (2) Diesel,
Engine type 4 stroke,
where: p - pressure drop across the cooler; direct injection
6-cylinder,
pu - air pressure upstream the cooler; pd - Cylinder configuration
in line
air pressure downstream the cooler. Bore x Stroke [mm] 102 x112
The processes in the cooler should be a Displacement [L] 5.5
trade-off between cooling effectiveness, Compression ratio 17:1
involving values as higher as possible Rated power [kW] 98
and flow restrictions, involving p values Rated speed [rpm] 2800
as lower as possible. Max. torque [Nm] 412
The present paper describes a stage in Max. torque speed [rpm] 1800
the R&D work aiming to increase diesel
engine performance, applied to a heavy The tests were performed according to
duty direct injection engine used for Romanian engine testing standard [6]
commercial vehicles, by implementing the which is equivalent to ISO 1585 [7].
air charge intercooling on a turbocharged During engine testing the ambient
engine. The main results of research work temperature was 15 C and atmospheric
were quantified reported to the pressure was 719 mm Hg.
performance of the turbocharged engine The engine was equipped as follows:
version; the newly developed engine- - 6 blade cooling fan 530 x 80 mm;
turbocharged and intercooled should have - no compressor and unloaded alternator.
higher rated power, maximum torque and The opacimeter used was Hartridge
reliability as well as lower specific fuel MK3 which has the effective length of
consumption, at the same or lower smoke measurement tube of 430 mm and
emission. Also the parameters of cooling readings in HSU (Hartridge Smoke
are assessed in terms of effectiveness (Eq. Units) or m1.
1) and pressure loss (Eq. 2). The engine performance (power, torque,
hourly and specific fuel consumption) has
2. Engine Test Procedure been measured on the 300 kW MEZ-
VSETIN dynamometric test bench at Road
The tested engine was manufactured at Vehicle Institute Braov (INAR) [8], as
Roman Truck Company (Braov, Romania), can be seen in Figure 1. The air cooler was
being a turbocharged direct injection engine placed in front of the engine coolant
798-05, having the series number 4538. radiator, similar to the positioning on the
The newly developed engine, vehicle.
abbreviated 798-05R, derives from 798-05, In order to compensate the effect of
having applied charged air intercooling increased power on the engine reliability,
and derating. The engine parameters before the engine was derated, the rated speed
intercooling are described in Table 1 [4]. being reduced from 2800 rpm to 2500 rpm.
The 798-05R engine was instrumented The engine was previously running in for
with temperature sensors measuring cooling 20 hours. The air intake system provided a
liquid, oil and exhausts gas temperatures, pressure loss of 270 mm column H2O and
Sandu, V.: Improving Diesel Engine Performance by Air-To-Air Intercooling 21

the exhaust system 370 mm column H2O, Heat exchanger parameters Table 2
meeting the product specification.
Cooler material Aluminum
Reference no. 89.08101.6007
Fin shape undulated, 0.5 mm thick
Tube shape rectangular
Frontal area [m2] 0.203
Mass [kg] 18
Dimensions [mm] 676 x 300 x 60

B. Engine speed characteristics at total

load (power, torque, hourly fuel
consumption, specific fuel consumption,
smoke emission).
Fig. 1. Intercooled engine during testing
Engine configuration is presented in
Figure 2. The engine was provided with
The charge air cooler was made of
M30 Super 2 lubricant.
aluminum being placed in front of the
liquid cooler, its main parameters being
3. Interpretation of Results
presented in Table 2.
The engine tests included two types of
A. The thermodynamic parameters of
measurements:
charge air and exhaust gas have been
A. Thermodynamic parameters of measured in order to find out the
charge air and exhaust gas (air effectiveness of the charge cooler. There
temperature at cooler intake and engine were measured the air temperature at
intake, exhaust gas temperature cooler intake, T2, and at engine intake, T3,
upstream and downstream the turbine, with the engine running at full load, over
as well as pressure loss on the cooler); the whole range of speeds.

Fig. 2. Configuration of turbocharged-intercooled diesel engine

22 Bulletin of the Transilvania University of Braov Series I Vol. 7 (56) No. 2 - 2014

Figure 3 illustrates the evolution of The air charge pressure loss varied in
temperatures, being obviously that the the range of 0.007-0.049 bar, as it can be
difference of temperatures, (T2 T3), is seen in Figure 5, the mean value being
significant, the air cooler lowering the air 0.025 bar.
charge with a mean difference of 39 C. According to literature [5] the maximum
The typical values of cooler effectiveness pressure loss for motor vehicle engine is
are 0.6-0.7, the higher values meaning that 0.1 bar, confirming the fact that the air
air charge is more intensely cooled [5]. cooler does not introduce too much
pressure loss. The measured exhaust
temperature downstream turbine plotted in
Figure 6 confirms the usefulness of
turbocharging, being lowered in average
with 63 C.

Fig. 3. Air temperatures versus speed

Fig. 6. Exhaust temperature versus speed

The reduction of air charge temperature

in combustion chamber implies the
lowering of exhaust gas temperature, as
Figures 3 and 6 show, predicting also
lower NOx emission in exhaust gas.
Fig. 4. Cooler effectiveness versus speed
B. Engine speed characteristics at total
Figure 4 illustrates the values of cooler
load required the measurement of torque,
effectiveness which meets the recommended
speed and smoke and the calculation of
range for speeds higher than 1500 rpm.
power, hourly and specific fuel
consumption. The results of the tests are
presented having as reference the
performances of the basic engine 798-05,
in Figures 7-11.
The engine power is represented in
Figure 7, showing significant increase of
rated power.
The engine torque gain is evident and its
profile shown in Figure 8 indicates a better
torque rise, the engine accomplishing its
Fig. 5. Air pressures versus speed work more rapidly.
Sandu, V.: Improving Diesel Engine Performance by Air-To-Air Intercooling 23

Fig. 7. Engine power outputs at full load

Fig. 10. Specific fuel consumptions

in function of engine exhaust gas flow.

Figure 11 illustrates a fair reduction of
smoke emission.
As smoke emission at 1400 rpm is pretty
closer to the threshold value, further
research work is required for optimisation
Fig. 8. Engine torque outputs at full load of engine operation at low speeds,
introducing more air by means of modified
The increase of hourly fuel consumption turbocharger housing or waste gate.
seen in Figure 9 is natural as the gain of
power is higher.

Fig. 11. Engine smoke emissions

Fig. 9. Hourly fuel consumptions 4. Conclusions

The real indicator of engine efficiency is The testing of the newly designed air-to-
the specific fuel consumption, plotted in air cooler proved to be appropriate for
Figure 10, which indicates for the engine intercooling in terms of
intercooled engine 9 g/kWh reduction and effectiveness and pressure loss.
a shift towards lower speeds corresponding By mild intercooling the newly developed
to maximum torques. engine - turbocharged and intercooled
The smoke emission was measured (798-05R) demonstrated 15 kW higher
according to prescription of ECE R24 rated power (15%), 100 Nm higher
Regulation [9] which indicates limit values maximum torque (30%) and 9 g/kWh
24 Bulletin of the Transilvania University of Braov Series I Vol. 7 (56) No. 2 - 2014

(5.7%) specific fuel consumption lower 4. Sandu, V., Ungureanu, V.B.:

than the turbocharged version (798-05), at Experimenting Charge Air Coolers
lower smoke emissions. Performance on the 798-05R
Turbocharged Diesel Engine. In:
Acknowledgements Proceedings of the Second Edition of
Motor Vehicles and Transportation
The author is grateful to research Conference, Timioara, 2012.
engineers A. Gal and N. Lungu for useful 5. http://www.turbobygarrett.com.
support and discussions. The Department of Accessed: 06-09-2014.
Engine Testing of Road Vehicle Institute 6. *** STAS 6635-87: Internal Combustion
Braov is gratefully acknowledged for Engines for Motor Vehicles. Rules and
research facilities. Methods for Bench Testing.
7. *** ISO 1585:1992: Road Vehicles -
References Engine Test Code. Net Power.
8. *** Study no. 33663, Road Vehicle
1. Challen, B., Baranescu, R., (ed.): Institute INAR Braov: Cercetare
Diesel Engine Reference Book. Oxford. pentru dezvoltarea motorului 154
Butterworth-Heinemann, 1999. CP/2500 rpm (Research Work for the
2. Hlavna, V., Kovalcik, A., et al.: The Development of 154 HP/2500 rpm
Influence of Intensity of Charge Air Engine).
Intercooling On Diesel Engine Gas. 9. *** ECE-R 24.03 Uniform Provisions
In: Journal of KONES Powertrain and Concerning the Approval of the
Transport 18 (2011) No. 2, p. 179-183. Compression Ignition Engines with
3. Mollenhauer, K.: Handbook Diesel- Regard to the Visible Pollutant
motoren. Berlin, Springer Verlag, 1997. Emissions of the Engine.