Application

Engineering
Bulletin
Subject: Air-to-Air Charge Air Cooling System for This AEB is for the following applications:
Cummins G-Drive Engines
Automotive Industrial Power Generation
Author: Curtis Kwasniewski

Date May, 2000 Page 1 of AEB Number 92.02

Engine Models included: All

Fuel Systems included: All

1
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Table of Contents

INTRODUCTION...........................................................................................................................................3

SELECTION & INSTALLATION................................................................................................................... 4

ATA Cooler Sizing................................................................................................................................................4

Air-to-Air Piping Selection ...................................................................................................................................5
Hoses .....................................................................................................................................................................6
Clamps....................................................................................................................................................................7
ATA Cooler Mounting ..........................................................................................................................................7
System Cleanliness.................................................................................................................................................9
Cooler Selection .....................................................................................................................................................9
ADDITIONAL CONSIDERATIONS........................................................................................................... 10
Cooling Fan Performance.....................................................................................................................................10
Cold Weather Operation.......................................................................................................................................11

VERIFICATION TESTING........................................................................................................................... 12

Equipment Required.............................................................................................................................................12
Test Preparation....................................................................................................................................................12
Test Method..........................................................................................................................................................14
Interpreting the Results.........................................................................................................................................15

INSTALLATION REVIEW CHECK LIST ......................................................................................................16

2
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

INTRODUCTION

Many of Cummins new G-Drive engines require the use of a heat exchanger that uses air
to reduce the Intake Manifold Temperature (IMT). This type of heat exchanger is termed
an “Air-to-Air Charge Air Cooler”.

The Air-to-Air Charge Air Cooling (referred hereon as ATA CAC) system flow is from
the outlet of the turbo (heated, compressed air) to the cooler, which acts as an air to air
heat exchanger, to the intake manifold (cooler, denser, compressed air)

The engine turbocharger supplies air to the engine cylinders at elevated pressures. In the
turbo-compressor the intake air is heated by compression. The ATA CAC system
removes some of this heat from the air before delivering it to the cylinder. The ATA
CAC system increases the density of the airflow. This has the effect of increasing engine
power capability, reducing exhaust gas emissions, and reducing thermal loading on the
engine power cylinder.

3
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

The purpose of this document is to provide the Cummins Engine Company requirements
and recommendations for selection, installation, and verification testing of an ATA CAC
system. Recommendations are intended to be used by the genset designer in developing
an efficient and robust system that will meet Cummins requirements with minimum size
and cost.

While this document specifies performance of specific components, Cummins will not
attempt to establish detailed durability test requirements. The performance of the ATA
CAC system is critical to the durability, performance, and emissions compliance of the
engine. Failure of the system could cause power loss, increased emissions, and possible
engine damage. The equipment manufacturer is responsible for the selection, design, and
installation per these requirements.

SELECTION & INSTALLATION

The ATA CAC system must satisfy the following requirements.

• The ATA cooler must be sized to maintain Intake Manifold Temperatures within the
limits specified on the Engine Data Sheet.

• The system must utilize proper piping, hoses, and clamps.

• The system must be mounted to allow for thermal expansion and contraction

• The system must meet cleanliness requirements

• The system must be of robust construction.

In addition the following features are recommended for an ATA CAC system.

•A means for monitoring intake manifold air temperature (IMT).

(Note: this is standard fo r engines with the Generator Drive Control System- GCS)

• Condensate drains.

ATA Cooler Sizing

The Engine Data Sheet contains the information necessary to select the cooler for the
ATA system. This information includes:

• Combustion Airflow

•Turbocharger Compressor Outlet Temperature

4
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

•Turbocharger Compressor Outlet Pressure

•Maximum Temperature Rise from Compressor Inlet (Ambient) to Intake Manifold.

•Maximum Allowable Intake Manifold Temperature.

• Heat Rejected to the aftercooler.

•Maximum Air Pressure Drop from Turbo Air Outlet to Intake Manifold.

From this information the cooling package manufacturer will be able to adequately size
the cooler.

Air-to-Air Piping Selection

ATA CAC system piping must be carefully selected to withstand the cyclical pressure
and temperature variations it will experience. Cummins requires:

• Aluminized steel or internally and externally coated steel piping.

• All welds to be protected with high temperature rust preventative paint.

• All airflow direction changes be made with piping (not hoses).

Aluminum piping loses much of its strength above 400 F (204 °C) and has a greater
thermal expansion than the system clamps. This makes aluminum more prone to
deformation or failure at the temperatures experienced on the hot side of the system.
Aluminized steel and coated steel do not suffer from these problems.

If the piping is fabricated from multiple lengths welded together the welding process will
destroy the protective coating on aluminized steel. This coating is necessary to protect
the piping from corrosion, both internal and external. A high-temperature, rustpreventative
paint or similar treatment must protect these welded areas. Cummins
recommends using a minimal number of welds.

All changes in air direction should be done with piping rather than hoses. Hoses have a
tendency to blow off due to high boost pressures and temperatures. 90° bends should be
avoided in ATA piping as they are more prone to hose blow off. The ATA piping to and
from the cooler should include as few bends as possible. Any bends that are made should
be made with the optimum radius for the pipe diameter.

Pipe diameter needs to be balanced between pressure drop requirements and transient
response. Excessive pipe diameter can lead to sluggish engine transient response while

5
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

an overly restrictive pipe diameter can cause an unacceptable pressure drop. Typical
piping sizes range between 3 inch (7.6 cm) for the C series engines up to 4.5 inch
(11.4cm) for the QST30.

Cummins recommends the use of a full 360° hose bead on pipe ends to prevent hose
blow off. The bead radius should be a minimum of 0.100 in (2.5mm).

Fig. 3 Good Piping Arrangement:

All direction changes made with piping.

Hoses
Hoses used in the ATA CAC system must be able to withstand high boost pressures and
temperatures and maintain their flexibility to absorb any relative motion. If hoses are to
run in close proximity to exhaust piping then the hose must be protected from the heat.

Cummins recommends the use of Nomex reinforced, bellows type, silicone hoses with
external reinforcing rings. Bellows–type hoses with external reinforcing rings control
hose “ballooning” yet remain flexible under high boost pressures. Table 1 lists the
pressure and temperature hoses must be designed to withstanding based on diameter. Do
not use fiberglass-reinforced hoses in the ATA CAC system.

Diameter in. (cm) Pressure PSIG (Kpa) Temperature °F (°C)

3.0 (7.6) 60 (415) 399 (204)
3.5 (8.9) 55 (380) 500 (260)
4.0 (10.2) 50 (345) 500 (260)
4.5 (11.4) 45 (310) 500 (260)

Table 1

6
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Clamps

The use of one high quality clamp per joint is normally acceptable. Cummins requires
the use of T-bolt style clamps with a torque retention feature and a bridge section below
the mechanism (SITB type clamp per SAE Standard J1508).
The torque retention feature is necessary to maintain clamp load even with silicon hose
creep. The bridge section will avoid the possibility of “hose puckering” under the clamp.

The use of additional types of retention elements is required at every hose joint for those
engines in which bosses are provided at the compressor outlet and intake manifold. (Such
as the QSX15)

ATA Cooler Mounting

The ATA cooler should be mounted in accordance with the cooler manufacturer’s
recommendations, including provisions for thermal expansion and contraction. Failure to
mount the cooler properly may result in premature ATA cooler fatigue failure due to
thermal stress.

7
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

There are two common arrangements used to mount ATA coolers. Provided that all
engine and ATA CAC requirements are met, either arrangement is acceptable.

1. Coolers mounted in series.

In this arrangement, the ATA cooler must be upstream of all other heat exchangers so
that it receives the lowest temperature cooling air. Care must be taken in this
arrangement to minimize debris entrapment between the two cores. Debris, may pass
through the less dense ATA cooler fins, but become entrapped by the high-density engine
radiator fins. Cummins recommends the equipment manufacturer install seals between
the two coolers, and/or match the fin density so debris will pass through both.

Since the fan airflow must pass through both coolers, greater system efficiency results by
smoothing the transition between the two. This is accomplished by matching the size and
shape to of the coolers as closely as possible. Because the ATA cooler is often smaller
than the engine radiator, the designer must consider the size of the ATA cooler. The
ATA cooler tanks should cover a minimal amount of the radiator core area. This results
in a more balanced fan airflow and better system efficiency.

2. Coolers mounted in parallel.

8
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

In this arrangement the ATA cooler and other heat exchangers should be mounted so that
the cooling airflow restriction is balanced across the fan sweep. This will maximize the
fan efficiency. Unbalanced restriction can lead to increased fan noise and may affect fan
durability.

System Cleanliness

During the construction of the ATA CAC system contaminants can be introduced.
Internal cleanliness is essential to the proper operation of the system.
The inspection method outlined in SAE Standard J1726 should be used to measure the
internal contamination level of the ATA cooler. The maximum total allowable internal
contamination for the cooler is 25 mg. Maximum allowable particle size is 0.125
in.(3.175 mm) The maximum total contamination for a complete circuit (including
cooler, hoses, and piping) is 90 mg. Failure to meet these requirements can seriously
affect engine durability as any contamination will be ingested directly into the engine
cylinders.
Cummins recommends the use of drains in the ATA CAC system. This will allow
periodic draining of condensate from the system.

Cooler Selection

In order to meet the requirement of a robust cooler construction, Cummins recommends

the use of cast ATA cooler end tanks. ATA coolers with brazed aluminum cores and cast
aluminum end tanks have proven reliable in the past. Fabricated end tanks can be used
but must be carefully designed and constructed to avoid failure caused by the cyclical
temperature and pressure changes experienced.

To reduce the occurrence of ambient air side plugging and therefore the frequency of
cooler cleaning, Cummins recommends coolers with no greater than 8-10 non- louvered
fins/inch. Cooler manufacturers have developed fins that use ripples or bumps rather

9
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

than louvers for fin turbulation. This design makes these fins less prone to fouling and
much easier to clean once fouled.

ADDITIONAL CONSIDERATIONS

Additional considerations in the selection of an ATA CAC system are the cooling fan
performance and the possibility of cold weather operation.

Cooling Fan Performance

The addition of an ATA cooler to a cooling package can create special requirements for
the engine-cooling fan. Optimizing the relationship between the fan, shroud, and cooler
areas can maximize the heat transfer performance of the radiator and ATA cooler.

Typically a blower fan arrangement is utilized. Because a blower fan draws air across the
engine, the cooling air passing through the ATA cooler will be warmer than ambient.
Using a blower fan arrangement may require a larger ATA cooling core and possibly
more fan airflow. In remotely cooled applications suction and blower fan arrangements
are similar in effectiveness.

The airflow through the coolers can be improved by matching the fan sweep to the cooler
area. This occurs when the fan sweep diameter equals or is slightly smaller than the
minimum cooler dimension (Fig. 9). Fan performance rapidly degrades as the fan
diameter exceeds the cooler dimension. This is due to the blockage of the airflow by the
cooler tanks. Cummins recommends at least a 4- inch (10.2 cm) gap between the fan and
cooler. This ensures good airflow distribution across the coolers.

Fig. 9 Fan Sweep

Another way to improve system efficiency is by using a shroud on the fan. A shroud
helps to channel the air between the fan and coolers and minimizes air recirculation at the
fan tips. Cummins requires a shroud design that smoothly transitions between the
rectangular cooler and the circular fan.

10
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Optimal fan performance can be achieved when fan-tip clearance is less than 2.5% of the
fan diameter (greater fan-tip clearance is required for engines with soft mounts).
Additionally, the fan should be immersed about 1/3 of the fan depth into the shroud. 33%
fan immersion is a general rule and may not apply in every installation. Proper fan
immersion should be determined by testing.

Airflow through the system can also be improved by minimizing obstructions in front of
or behind the fan, particularly near the fan perimeter where airflow is the greatest. These
obstructions can disrupt the airflow and distance to them should be maximized where
possible.

Cold Weather Operation

Generator sets operating in very cold climates must be equipped with special provisions
to prevent the overcooling of the intake air. Overcooling of the intake air can lead to
such problems as white smoke, poor performance, and decreased durability. In the event
that an engine will be operated in a continuously cold environme nt the ATA CAC system
should be appropriately designed.

For gensets used in cold environments, provisions should be made to draw cooling air
from over the engine, or in the case of an enclosed generator from inside the engine
compartment. Additional equip ment to consider utilizing are thermostatically controlled
fans and louvers. This will help prevent excessively cooling the intake air.

11
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

VERIFICATION TESTING

ATA CAC system verification testing should be conducted in conjunction with the
verification testing for the engine radiator system.
The following two criteria must be met in order to ensure the system meets Cummins
requirements.

1. The difference in the temperature of the intake air entering the intake manifold to
that of the ambient air is less than or equal to the value on the data sheet.

2. The pressure drop across the entire ATA CAC system is less than or equal to the
value on the data sheet.

Equipment Required

1. Load Bank or similar means of loading the generator.

2 A minimum of two thermocouples (Type E).

3. A minimum of two pressure gages or manometers capable of measuring 100 in.

(2540mm) Hg or a differential pressure gage capable of measuring 10 in.(254mm)
Hg.

4. A means of monitoring and recording the temperature and pressure readings.

Test Preparation

1. Control air temperature on core between 70°F and 110° F (21-43 ° C)(preferably
above 90° F( 32°C))

2. Install a thermocouple in to monitor intake manifold temperature. (Using installed

ports in the intake manifold or in piping as shown)

3. Monitor ambient temperature at a location where radiated heat from the engine
will not be experienced. This is typically at least 3 feet (1m) away from the
engine, away from the exhaust system, and shielded from sunlight.

12
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Fig. 11. Recommended Ambient Measurement Locations.

(Marked as X)

4. Install pressure taps in the ATA piping near the outlet of the turbo compressor and
in (or near) the intake manifold. Do not use the same tap as the thermocouple.

5. Lock thermostatically controlled fans to full speed setting. (If Applicable)

6. Connect pressure gages or manometers to pressure taps.

7. Install all engine covers, grilles, louvers, etc.

8. Connect means of loading the generator.

9. Install monitoring equipment.

13
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Test Method

CAUTION
If at any time Intake Manifold Temperature (IMT) exceeds the value on the engine
data sheet unload the generator, discontinue the testing, and review the installation.

1. Start the engine and gradually increase the load, carefully monitoring IMT and
boost pressure, to full load (within 5%).

2. Allow a minimum of 10 minutes for IMT to stabilize at a maximum value.

3. ecord values of temperature and pressure at this stable full load.

4. Determine the pressure drop across the ATA CAC system and the air temperature
rise from ambient to intake manifold.

14
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

Interpreting the Results

Pressure drop and air temperature rise values from testing typically are within the
allowable limits defined on the Engine Data Sheet. If this is not the case the cause of the
out of specification parameter must be determined.

• Maximum Temperature Rise between Engine Air Intake and Intake Manifold
exceeded: In this case the ATA CAC system is not dissipating sufficient heat. In
higher ambient temperatures the IMT would rise above the limit listed on the Engine
Data Sheet. The causes of this condition may be as simple as insufficient cooling fan
flow or as complicated as improper design of the system. Additional testing is
required to pinpoint the cause.

• Maximum Air Pressure Drop from Turbocharger Air Outlet to Intake Manifold
exceeded: In this case the ATA CAC pressure at the Intake Manifold is insufficient.
This can lead to incomplete combustion reduced durability and performance, and
higher emissions. Possible causes could be air leaks in the system, or an overly
restrictive system design. Additional testing may be required.

15
Cummins Confidential
 Air-to-Air Charge Air Cooling System for Cummins G-Drive Engines

INSTALLATION REVIEW CHECK LIST

Initial Appropriate Box
YES NO Actual
Value
Prior to Initial Start:
1. Was internal contamination less than 90 mg?
Performance:
1. Was air temperature rise within limits of Data Sheet?
2. Was system pressure drop within the limits of Data Sheet?
Core:
1. Is the cooler of robust construction?
2. Does the cooler mounting allow for thermal expansion and
contraction?
3. Does the cooler mounting allow for vibration?
4. Is the cooler isolated from the engine by using flexible hoses?
5. Is the cooler fin density 8-10 fins/inch?
6. (Parallel arrangement only) Is the fan airflow balanced across
the coolers?
7. (Series arrangement only) Is the ATA cooler exposed to the
cooling air stream first?
8. (Series arrangement only) Are the fin densities of the two
coolers matched?
9. (Series arrangement only) Is there a seal between the coolers?
10. Is there a proper shroud?
Piping
1. Is the system piping made of aluminized steel?
2. Are all system direction changes made with piping?
3. Are welds protected with high temperature rust preventative
paint?
4. Is the system adequately supported to prevent excessive
movement?
5. Do hoses have 360° continuous hose bead at pipe ends?
Hoses and Clamps
1. Are hoses used that meet temperature and pressure
requirements?
2. Are system clamps T-bolt style with a torque retention device
and bridge section? (SAE type SITB clamps)
Cold Weather
1. Does the system arrangement allow for drawing intake air from
across the engine?

16
Cummins Confidential