development and practical experience of … · a single engine family, such as the maxxforce® 7,...

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DEVELOPMENT AND PRACTICAL EXPERIENCE

OF A 2010 COMPLIANT HEAVY DUTY DIESEL

ENGINE AND AFTERTREATMENT SYSTEM

Dr. Brad Adelman, Ed Derybowski, Victor Miranda, Matt Tyo

Navistar, Melrose Park, Illinois, USA

Jan Kramer, Claus Bruestle

Emitec, Inc., Rochester Hills, Michigan, USA

20. Aachen Colloquium Automobile and Engine Technology 2011

_________________________________________

20. Aachen Colloquium Automobile and Engine Technology 2011 2

Summary

To meet the 2010 EPA particulate matter emissions limit of 0.01 g/hp-hr, Navistar has

chosen to equip its new 2010 MaxxForce™ engines with a compact and highly

efficient aftertreatment system consisting of a metallic Diesel Oxidation Catalyst (DOC)

and a wall flow Diesel Particulate Filter (DPF).

The DOC and DPF were optimized to fit into small packaging spaces which are

installed under a variety of customized truck cab designs. The exhaust aftertreatment

system was designed and tested for reliable operation over the full vehicle life of more

than a million miles. By using a new metallic DOC with advanced turbulent LS design

® it was possible to improve the exhaust flow mixing and mass transfer within the

DOC catalyst substrate.

Navistar’s Engineering teams used these benefits and were able to design a DOC with

a lower cell density, minimizing backpressure and the risk of face plugging. At the

same time, the DOC substrate volume and amount of precious metal (PGM) could be

reduced significantly, lowering the overall package and system cost.

This paper describes the development, emission performance testing and mechanical

robustness testing of the new Navistar 2010 exhaust aftertreatment system, with a

focus on the DOC. A first practical experience and feedback from vehicle operation

with the new turbulent metallic DOC will be discussed.


1 Introduction

The adoption of US2010 standards, marked the introduction of the world’s most

stringent emission limits for on-road heavy duty diesel engines. Significant reductions

in particulate matter (PM) and nitrogen oxides (NOx) where instituted when compared

to the US2004 standards. In 2007, diesel particulate filters (DPF) and exhaust gas

recirculation (EGR) to meet the PM and NOx standards, were accepted universally.

Most engine manufacturers incorporated selective catalytic reduction (SCR) of NOx

using an aqueous urea solution (DEF) in addition to the DPF in order to achieve

compliance with the US2010 emission limits for NOx. Urea based SCR has proven to

be very efficient in NOx removal but also suffers from many deficiencies such as

inadequate urea conversion to ammonia at low exhaust temperatures or lack of

inducements if DEF is not available. As a result, it is possible for these urea based

SCR engines to produce NOx emissions that greatly exceed the US2010 limits.

Figure 1: US and EU HD Diesel emission legislation

Navistar has been able to avoid all of these limitations by not requiring any NOx

reduction technologies across the entire range of their MY2010 engines. In order to

accomplish this task, Navistar has incorporated advanced combustion techniques to

achieve engine out NOx emissions below the US 2010 limit. While the NOx emissions

were achieved via engine control, the key challenge for Navistar was the increased

burden placed on the DPF system.

Filter regeneration relies on two mechanisms. The first is based on the oxidation of

soot by NO2. This is generally considered as “passive” regeneration. Under idealized


drive-cycles which provide exhaust gas temperature above 250°C and NOx to soot

ratio greater than 20/1, it may be possible to operate the vehicle in a manner where

the rate of soot accumulation in the filter is less than the rate of soot oxidation. OE

applications for 2010, however, span a wide and nearly unpredictable range of in-use

cycles and all are equipped with a DPF. As such, the DPF systems cannot rely on

passive regeneration to maintain a clean filter. Therefore, engine-based intervention

measures have been employed to ensure filter regeneration under all vehicle driving

conditions. Such “active” systems were introduced on passenger cars in Europe in

2000 and are currently in wide spread usage throughout the European and Japanese

diesel passenger car segment and all US commercial vehicles since 2007 [13,14].

These active systems utilize engine-based heating and regeneration strategies using

either in-cylinder or in-exhaust post injection of fuel, in combination with advanced

controls.

Whether the added fuel is injected in-cylinder or in-exhaust, a diesel oxidation catalyst

is required to convert the chemical energy of the fuel into thermal energy. The design

of the DOC is critical in achieving safe and efficient DPF regeneration as well as

proper integration into the vehicle packaging. The primary objective of this paper is to

determine the best substrate design for the DOC as well as to quantify the HC and NO

conversion across the DOC. This paper will also address improvements to the DPF,

which are afforded from improvements in the DOC. Data are presented from engine

dynamometer and vehicle testing.

2 Components of the Navistar 2010 Aftertreatment System

In order to comply with the 2010 US Emission regulation, all 2010 MaxxForce®

engines are employing sophisticated engine strategies combined with cost effective

emission control aftertreatment technology. Instead of SCR, Navistar is addressing

2010 emissions requirements for its core applications through advanced air- and fuel-

management technologies and exhaust-gas recirculation (EGR) systems. Possible

incremental NOx after-treatment components are avoided, and the proven

combination of Diesel Oxidation catalyst (DOC) and Diesel Particulate Filter (DPF)

was further developed and refined to achieve better performance at lower system cost,

see Figure 2.

Additionally, adopting an engine based strategy to achieve the 2010 NOx emission

limits allows the carry-over of 2007 aftertreatment packaging and controls strategy

from 2007 when DOC/DPF systems were first mass introduced to the US medium-

and heavy- HD market. A single engine family, such as the MaxxForce® 7, may have

over 100 various exhaust configurations.


Figure 2: Diagram of US 2010 aftertreatment installed on a Prostar® vehicle with a

MaxxForce® 13 engine

Engine Cylinders Displacement Power Torque

MaxxForce 7 V-8 6.4 L 220 – 300 hp

(164 – 224 kW) 560 – 660 lb.ft. (760 – 898 Nm)

MaxxForce DT Inline 6 7.6 L 215 – 300 hp

(160 – 224 kW) 560 – 660 lb.ft. (760 – 898 Nm)

MaxxForce 9 Inline 6 300 – 330hp

(224 – 246 kW) 860 – 950 lb.ft.

(1116 – 1288 Nm)

MaxxForce 10 Inline 6 9.6 L 310 – 350 hp

(231 – 260 kW) 1050 – 1150 lb.ft. (1423 – 1559 Nm)

MaxxForce 11 Inline 6 11 L 330 – 390 hp

(246 – 291 kW) 1250 – 1450 lb.ft. (1693 – 1964 Nm)


(306 – 354 kW) 1450 – 1700 lb.ft. (1964 – 2302 Nm)


(324 – 410 kW) 1550 – 1800 lb.ft. (2099 – 2505 Nm)

Table 1: US 2010 Engines for truck and bus applications [12]

Soot oxidation may occur via two dominant reactions. One path relies on high

NOx/soot ratio and exhaust gas temperatures above 250°C. In this process, NO is

oxidized to NO2 over the DOC and then NO2 oxidizes the soot on the filter.


The result of the reaction is CO and NO evolution. If the filter is catalyzed, then the NO

can be recycled to remove additional soot. This process is very dependant on both

drive cycle (exhaust gas temperatures) and engine out emissions. For engines that

meet the US 2010 NOx regulations via combustion parameters, the engine out NOx

concentrations is too low to ensure continuous regeneration of the filter under all

circumstances. Therefore, periodic, forced or “active” regenerations of the

accumulated soot in the filter are necessary. Active regeneration of the filter is required

even with engines equipped with NOx aftertreatment.

To manage the active regeneration events, the aftertreatment system needs to be

closely integrated in the vehicle and engine management systems to ensure operation

of the filter within its capability window. This requires precise control of the filter inlet

conditions (temperature/flow/HC concentration) and soot load level. Once the DPF

algorithm determines regeneration is required, the inlet temperature of the filter must

be increased to the point where soot oxidation with O2 occurs (Figure 3).

Figure 3: Integration of DPF in engine/vehicle controls [11]

One method to achieve this is the injection of additional fuel, which is combusted over

the DOC. The added fuel may be from an in-cylinder injection event, which occurs

after the combustion event to prevent fuel burning before the DOC, or fuel may be

injected directly into the exhaust. The benefit of the latter is that it prevents oil dilution

and engine wear, while in-cylinder injection avoids additional injection hardware and

supports mixing and vaporization of the fuel before entering the DOC.


2.1 Diesel Oxidation Catalyst

Diesel Oxidation Catalysts have been used since Euro 2/3 vehicles and US HD Diesel

engines from 1994 or later and will remain a common component of modern Diesel

exhaust aftertreatment systems. Initially used to reduce harmful HC and CO

emissions, the DOC is designed today to address a much broader and more complex

series of functions, including:

• Oxidize HC and CO from the engines exhaust gas

• Oxidize NO to NO2 to support passive PM-Filter regeneration and fast SCR

reaction

• Partly reduce PM emissions by oxidizing soluble organic fractions (SOF)

• Burn injected fuel to increase exhaust temperature for PM-Filter regeneration

To support these functions with a high degree of performance and at the lowest

possible cost, both the DOC substrate and the catalyst for the 2010 MaxxForce®

engines were specifically designed and matched to each engine and application.

Special attention was given the DOC substrate, and the following key requirements

were defined during the product development process:

• Provide high masstransfer and sufficiently large surface area for washcoat

• Minimize DOC backpressure and risk of face plugging, select thinnest possible

catalyst walls and largest possible open frontal area (OFA)

• Provide highest mechanical robustness to vibration loads and thermal shocks

over the life of the truck, typically 1.5M miles, and under most severe altitude

and environmental conditions

• Minimize packaging space, system weight and cost by selecting the smallest

possible DOC volume

The final production DOC design is the result of a compromise between several

counteracting design characteristics, with the focus on reliable and high DOC

performance to comply with emissions regulation over the full warranty life, up to

435,000 miles for Heavy HD trucks.

2.2 Diesel Particulate Filter

To meet US 2007 emission limits, diesel particulate filters were introduced on all

engine applications. The wall flow-through design of the DPF allows for the very high

trapping efficiency required to meet the 0.01 g/bhp.hr tailpipe limit. Though the design

of the filter may vary in volume, aspect ratio, soot mass limit and use of a catalyst,

some common design characteristics can be summarized. Ideally, the DPF selection

should have minimum impact on engine performance. Increasing exhaust restriction

and raising the exhaust temperature for active regeneration may result in an increase

in fuel consumption.


This has led to the tendency of HD applications with filter volumes roughly twice the

engine displacement. Larger filters may minimize exhaust restriction but may be more

difficult to package and may result in uncontrolled regeneration events as heat is

propagated down the length of the filter during an active regeneration event.

For systems that do not have NOx aftertreatment, such as all Navistar US 2010

engines, filter design has utilized unique filter materials, which allow for an increase in

the quantity of soot stored between regeneration events, lower pressure drop and

increase in durability (thermal stresses during interrupted regeneration events).

Further discussion on the nature of the filter material is not the focus of this paper.

The integration on the DPF and DOC, however, are critical in the selection of

aftertreatment hardware. Ideally, all the fuel added to the exhaust for active

regeneration is oxidized over the DOC. This prevents both additional temperature rise

on the DPF when the thus slipped HC is oxidized on the DPF, as well as HC

accumulation in the soot cake if the DPF temperature is below the lightoff temperature.

Also, complete conversion of the dosed HC allows greater accuracy in the inlet

temperature to the DPF as well as the predicted outlet temperature which, in turn,

minimizes the risk of filter damage and allows for less frequent regeneration events as

higher soot loadings can be allowed without the commensurate risk of excessive

temperature during active regeneration. Unfortunately, a DOC which ensures complete

oxidation of the dosed fuel, would be prohibitively costly (high precious metal content)

and large.

The focus of this paper will be the performance of the DOC over various drive cycles

with special attention to designs that minimize HC in both fresh and fully aged states.

3 System development and optimization

3.1 DOC substrate design

The overall performance or conversion efficiency of a catalyst system, as measured on

standard emission test cycles, is a combined result of the applied catalyst and

substrate technology. Depending on the operating temperature, several chemical and

physical processes are the limiting mechanisms for a DOC’s performance. While the

exact behaviour is different for each catalyst technology, it can be commonly illustrated

as shown in Figure 4.

Beginning at the light off temperature, the chemical reaction kinetics of the catalyst are

the primary limiting factor, and conversion efficiency in this regime is influenced mainly

by the mass and dispersion of the catalyst precious metal. At intermediate

temperatures, the rate of catalytic reaction is limited mostly by the speed at which

reactant and product molecules diffuse through the pore system of the washcoat to the

active sites with precious metal. This mechanism is generally defined as pore

diffusion.


Finally, at higher temperatures, the catalytic conversion rate is controlled by bulk mass

transfer, or the rate at which reactants diffuse through a stagnant layer of gas in the

catalyst channel, the boundary layer, to reach the catalyzed channel wall.

Figure 4: Example illustration of conversion rate limiting steps of heterogeneous

catalysis [1]

The following chapter focuses on methods to increase mass transfer by optimizing the

catalyst substrate design.

Equation (1) describes the relationship between catalytic efficiency, masstransfer

coefficient (β), geometrical surface area (GSA) and hydraulic diameter (dh) for the

mass transfer limited operation at high temperatures.

�� 1 � exp � ∗� �� (1)

For the gas flow in a catalyst channel, the masstransfer coefficient can be calculated

as a function of the Sherwood number (Sh), Reynolds number (Re) and substrate

geometry (dh, L), see Equations (2), (3), (4) and (5). [7]

� � ��∗ �� (2)


�� g

ec

Gzf

Gzd

baSh

+

+

1

Re

1lim (3)

�� L

dhScRe (4)

�� ∗�� !!!∗" (5)

Where D12 = binary diffusion coefficient (based on CH3)

Shlim = limiting Sherwood number

a, b, c, d, e, f, g = constants

Sc = Schmidt number

L = catalyst channel length

v = kinematic viscosity

w = gas channel velocity

A traditional method to increase the catalytic efficiency (1) is the use of catalyst

monoliths with higher cell densities, which provide both more GSA and at the same

time reduce the hydraulic diameter of each catalyst channel. Figure 5 below illustrates

this effect, calculated for equal volume substrates with 0.05mm foil thickness under

mass transfer limited conditions.

Figure 5: Calculated mass transfer coefficient and surface area for different cell

densities over gas velocity [7]


Because of the higher backpressure and higher risk of face plugging associated with

high cell densities especially for Diesel engines, a typical practical limit of 300cpsi or

400cpsi was widely adopted by the industry.

At the same time, a number of metallic substrates with advanced “turbulent” channel

designs were developed and introduced into the market in the past years. These

substrate designs, in particular the LS design ®, improve flow distribution and mass

transfer within the catalyst substrate [4, 5].

Figure 6: LS design used in the 2010 MaxxForce DOC substrates

The foil of an LS substrate as shown in Figure 6 is characterized by shovels protruding

into the flow channel which transform laminar exhaust gas flow inside the catalyst

channels into “turbulent” flow. As the exhaust gas is travelling through the catalyst

channel, each shovel entrance and exit represent a change in channel geometry,

preventing the development of laminar gas flow. This effect enhances the mass

transfer rate significantly- without the use of higher cell densities.

Several previous studies have shown that under typical operating conditions the LS

design ® can be used to downsize the DOC and reduce the required amount of PGM

by approximately 20-30%, while providing the same or better catalytic efficiency as a

larger standard DOC without penalizing exhaust backpressure [2, 3].


Using again Equations (1) through (5), the effect of the LS structure can be calculated

as shown in Figure 7. The example illustrates how a 300cpsi LS substrate can provide

higher catalyst efficiency, expressed here as the product of β * GSA, when compared

to 400cpsi standard channel substrates under mass transfer limited conditions.

Figure 7: Calculated mass transfer coefficient and surface area for LS foils and

standard foils over gas velocity [7]

3.2 DOC substrate layout

The LS design ® was chosen as a new technology and developed initially for the

application on the MaxxForce 7 ® engine. In a first step, the previous production DOC,

a 300cpsi straight channel substrate, was characterized and compared to several

alternative substrates. The alternatives included an equal volume 400cpsi substrate,

an equal volume and a downsized 300cpsi LS substrate.

For a practical comparison of the mass transfer performance of different catalyst

designs at representative exhaust gas conditions, the Effectiveness-NTU-Method was

applied [6]. With this method, Equation (1) was reduced to

�� 1 � exp#�$%&' (6)

with

$%& � ∗� �� (7)


The potential alternative catalyst substrates were compared based on their NTU for

high exhaust flow conditions of 1200kg/h and an exhaust temperature of 450 deg. C,

and assuming a uniform washcoat of 120g/L for each substrate, see Figure 8.

Figure 8: Mass transfer performance comparison based on NTU for different DOC

design alternatives

With the goal of DOC volume and PGM reduction for overall system optimization, the

downsized 300LS DOC substrate was chosen to replace the precious production

catalyst. Based on the NTU prediction, it was expected this DOC would provide a

similar or better catalyst efficiency while at the same time minimizing the catalyst

volume and required PGM. Table 2 lists key design characteristics of the previous and

new DOC substrates.

300cpsi Std.

Production DOC 300cpsi LS DOC

Improvement [%]

Volume [L] 3.8 2.9 -22%

GSA [m2/L] 2.2 2.6 18%

OFA [%] 65 85 30%

Heat capacity [J/L/K] 515 406 -22%

Table 2: Design characteristics of production DOC and optimized 300LS DOC,

assumption: coated with 120g/L

The combination of a moderate cell density of 300cpsi and the ultra-thin metallic foil

provide a significantly higher OFA than the production DOC, reducing the risk for face

plugging. The reduced thermal mass is expected to support faster warm up during the


initiation of a DPF regeneration. The 22% reduction of DOC volume allows not only a

lighter and more compact aftertreatment system, but especially offers a highly effective

design solution to reduce overall system cost. Figure 9 below illustrates the significant

potential for cost savings in dollars per engine swept volume (ESV) for three typical

DOC washcoat loadings from 40g/ft3 to 90g/ft3, based on a DOC:ESV ratio of 1:2.

Figure 9: Potential for system cost savings by downsizing a DOC using the LS Foil

design, example DOC:ESV = 1:2, volume reduction = 22%

3.3 DOC Performance testing

The initial emissions performance testing was conducted in three phases. First,

Hydrocarbon (HC) and Carbon Monoxide (CO) oxidation performance under standard

federal test conditions was recorded. The second phase included transient testing with

active DPF regeneration switched ON to investigate HC and CO conversion under

higher engine-out emissions. In a final step, emissions performance under stationary

DPF regeneration was measured, again focusing on HC conversion and slip as well as

DOC and DPF temperatures.

The new 22% smaller 300cpsi LS DOC was washcoated with the same specific

loading as the production DOC, and both catalysts were installed on an engine

dynamometer with the DPF removed. Each DOC was de-greened under full load

engine operation for eight hours. The DOCs were then tested with the Heavy Duty

Federal Fest Procedure (HD FTP).

The standard test cycle exhibited very low HC and CO engine-out emissions. The 2.9L

300cpsi LS DOC showed equal or better HC and CO oxidation performance compared

to the 3.7L production DOC in both test cycles, see Figure 10.


Figure 10: HC (magnified x10) and CO Emissions downstream of 3.8L production

DOC and 2.9L 300cpsi LS DOC in standard HD FTP

In the next phase of emissions testing, the engine was manually switched to DPF

regeneration mode during the transient HD FTP test, generating a significantly higher

HC engine-out concentration during some sections of the test cycle.

Figure 11: HC concentration downstream of production DOC and 300cpsi LS DOC

during HD FTP test with active DPF regeneration


Figure 11 shows the HC concentration upstream and downstream of each tested

DOC. Between 650 and 1000 seconds the DPF regeneration was switched active,

producing a very high engine-out HC concentration. Again, the 300cpsi LS DOC with

22% less volume and PGM showed a better HC oxidation performance compared to

the production DOC, indicated by the significantly reduced HC slip.

For the third test phase, a test cycle was designed to investigate temperatures and

maximum HC slip over the DOC during a simulated stationary DPF regeneration. A

MaxxForce DT engine was used for this test. The engine was set to a constant speed

of 1500/min and torque was adjusted to achieve a stable and constant exhaust gas

temperature of 300°C in front of the DOC. Upon stabilization of the system, in cylinder

HC dosing was initiated. The dosing rate was controlled to achieve a DOC outlet

temperature of 550-600°C.

Figure 12 discusses the results -the averaged data of two tests. The 300cpsi LS DOC

initially heats up faster as a result of its higher catalytic activity and lower thermal

mass, however, this may also be partly due to the slightly higher HC concentration

during this test. At fully warmed up condition and high HC inlet concentration, the 2.9L

300cpsi LS DOC allowed a HC slip of approximately 3%, while the larger 3.8L

production DOC slipped about 10%.

Figure 12: Stationary HC dosing test with 300cpsi LS DOC and production DOC


3.4 Washcoat development

Though detailed information about the washcoat is not available for publication,

general trends can be discussed. The focus of the development was to achieve similar

or improved HC conversion over the DOC compared to the 2007 baseline technology.

Both standard and turbulent substrates were studied and PGM cost reduction was

achieved either by shortening the length of the DOC or lowering the PGM loading. In

all cases, the improved 300cpsi LS DOC had about 23% less PGM than the 2007

baseline DOC.

Substrate PGM loading

(nominal) PGM per part

(nominal) Architecture

300cpsi Std. Baseline Baseline 7.5”X5.2” zoned

300cpsi LS 1.00 0.77 7.5”X4.0” uniform

400cpsi Std. 0.78 0.77 7.5”X5.2” uniform

400cpsi Std. 1.00 0.77 7.5”X4.0” zoned

Table 3: Washcoat loadings investigated during development

3.5 Durability testing

The system development phase included canning trials and confirmation of

mechanical robustness of the DOC substrate.

Critical stressors and design characteristics were determined and confirmed using an

ABAQUS Finite Elements (FE) model first. Based on the FE analysis, it was concluded

severe thermal shock, e.g. from rapid thermal cycling, is the most critical stress factor,

leading to a possible loss of mantle-matrix retention as the primary failure mode.

Figure 13 illustrates the critical area of the matrix near the mantle of the metallic DOC.

Special attention was paid when designing this particular section of the substrate to

withstand low cycle fatigue from thermal shock [9].

Derived from a survey of real world usage profiles and a Design Failure Modes and

Effects Analysis (DFMEA), a component bench test was used to investigate and

confirm the mechanical robustness of the metallic DOC substrate against vibration and

thermal shock [10].


Figure 13: FE simulation of thermo shock induced stress on the metallic DOC

substrate

The DOC substrate was installed in a 45 degree fixture onto an electromagnetic

shaker and exposed to random vibration, see Figure 14. The mechanical load level

was defined by a Power Spectral Density (PSD) envelop curve with an effective power

of 6g RMS between 10 and 2000Hz.

Figure 14: Emitec component durability test setup, Example: DOC for Maxxforce DT

engine


At the same time, a propane fueled gas burner supplied exhaust gas with a highly

transient temperature cycle to the substrate. While the temperature level was kept

close to real world conditions, the frequency and rate of heat-up and cool-down events

were significantly increased to accelerate the test, see Figure 15.

Figure 15: Temperature profile used during accelerated component bench test

Each substrate was tested with a sample size of three to six pieces for 100 hours, or

3200 thermo shock cycles, and then inspected for degradation. After this test duration,

no loss of mantle-matrix retention was allowed. A boroscope was used to inspect the

matrix near the mantle, the area which was considered critical after the FE analysis.

Very little or no degradation was found, see example in Figure 16.

In addition to the strictly mechanical component tests at Emitec, all substrates were

subjected to further rigorous testing during consequent washcoat durability tests or full

system durability tests at the next tier suppliers.


Figure 16: Example of boroscope inspection of a 300cpsi LS DOC substrate after 100h

of accelerated component bench test.

4 System validation

4.1 Aging test

After the emissions performance of the optimized LS DOC was confirmed for de-

greened condition, an accelerated engine aging test was conducted to investigate the

degradation in catalytic performance. Although it was expected that the substrate

material and design itself has no influence on degradation of catalytic performance

over time, it was necessary to investigate if the smaller DOC volume contributed to a

faster aging over time.

The catalysts were installed on a Maxxforce DT engine, and exposed to an

accelerated aging cycle. This cycle consisted of 20 minutes of DPF regeneration mode

with HC dosing active, followed by 10 minutes of high load engine operation.

Maximum temperatures in the DOC reached 600°C during the HC dosing, and about

350°C during normal engine operation. The combination of high load engine operation

and frequent fuel dosing events was chosen to simulate contamination from fuel and

lubricants, as would be expected over the life of the vehicle. The aging cycle was

repeated more than 600 times.

The aged 300cpsi LS DOC was tested in a HD FTP test cycle with Regeneration

switched ON, and HC oxidation performance was compared to results with the de-

greened production DOC and 300LS DOC, as shown in Figure 11.


It was found that its HC performance in fully aged condition was now slightly

degraded, which allowed a higher maximum HC slip, although still less than the de-

greened former production DOC, see Figure 17.

A full aging of the former production DOC was not conducted at this time due to limited

resources. It is known from previous development work that the production catalyst

aged at a similar rate as the 300cpsi LS DOC, and this degradation rate was

extrapolated from the de-greened data.

Figure 17: HC concentration upstream and downstream of de-greened 3.8L production

DOC and 2.9L 300cpsi LS DOC in de-greened and fully aged condition,

Average of data from HD FTP test, 800-850 seconds.

4.2 Face plugging test

A face plugging test was designed and conducted to study the new DOC substrate's

sensitivity to clogging under cold exhaust temperatures and high soot concentration.

The 300cpsi LS DOC is using a foil thickness of 0.04mm (1.6 mil), providing an OFA of

approximately 85% compared to 65% for the production DOC (see Table 2), and no

increased risk of face plugging or clogging was expected.

During the test, the 300cpsi LS substrate was exposed to low temperature exhaust

gas combined with frequent accelerations and fuel dosing events for an extended

period of time, and a visual inspection of the DOC front face was conducted at regular

intervals. After completion of the full test duration, the DOC was found to have no

significant soot accumulation on its front face as shown in Figure 18.


Figure 18: Front face of 300cpsi LS DOC after completed face-plugging test

5 Field testing

5.1 Proving ground durability vehicles

During the final phases of engine and calibration development, a number of

development vehicles at Navistar’s proving ground were equipped with production-

intent LS DOC substrates to accumulate miles under various operating conditions.

Two examples with distinct driving cycles are highlighted in the following section.

One particular vehicle was running a continuous highway cycle program at engine high

load and with frequent DPF regeneration events and DOC outlet temperatures of

650°C, until 100,000 miles were accumulated. At a specified interval, the

aftertreatment system was inspected, and the mechanical condition of the DOC was

documented. The goal of the inspection was to detect any possible onset of separation

of matrix foils from the mantle or any signs of face damage or plugging. No issues

were found.

A second vehicle was operated in a low load cycle to simulate typical city driving, as

expected with delivery trucks. The extended low temperature operation was

specifically designed to investigate the robustness of the aftertreatment system to

plugging. The DOC passed this test, and no issues were found, see Figure 19.


Figure 19: 300cpsi LS DOC removed from Maxxforce DT engine after completed City

Cycle program at proving ground

5.2 Road durability vehicles

Extensive road testing was conducted under most severe conditions to confirm the

durability of the new DOC, and a significant portion of the road tests included high

altitude operation with both urban and highway drive conditions.

A number of Navistar ProStar® trucks were operated in the mountain ranges at

altitudes of 5,000ft (1700m) to over 11,000ft (3350m) with fully loaded trailers, see

Figure 20.

The operation included manually induced DPF regeneration events under high load

and limited O2 availability. The DPF regeneration control strategies proved effective,

and all aftertreatment system temperatures could be maintained within their specified

ranges. This cycle was driven in the summer and winter months to determine the

impact of hot and cold ambient conditions on performance.


Figure 20: Altitude profile of the route used for high altitude road testing

At scheduled intervals, the aftertreatment systems of each truck were disassembled

and the DOC was inspected for signs of damaged foils, onset of matrix-mantle

retention or plugged cells. No problems were found, see example in Figure 21.

Figure 21: Main DOC of Maxxforce 13 truck at inspection during high altitude testing


6 Conclusions

• Navistar has successfully developed and implemented a 2010 compliant engine

and Aftertreatment system which does not rely on DEF based SCR.

• The system is robust for reliable active regeneration of the DPF even under

most severe conditions.

• Using a new turbulent metal DOC substrate technology has allowed for

significant PGM reduction by downsizing the required DOC volume without

sacrificing catalyst performance.

• Extensive Engine aging and vehicle testing have confirmed that the new,

smaller DOC meets the durability requirements of Heavy Duty On-highway

trucks.

• More than 100,000 new turbulent DOC substrates have been manufactured and

shipped since their introduction in Navistar’s 2010 MaxxForce engines. No field

failures have occurred.


7 References

[1] Ron Heck, Rob Farrauto, S. Gulati

“Catalytic Air pollution control”

John Wiley & Sons Inc,

New York, 2002

[2] M. Bollig, J. Liebl, R. Zimmer; BMW Group; M. Kraum, O. Seel, S. Siemund;

Engelhard Technologies GmbH; R. Brück, J. Diringer, W. Maus; Emitec GmbH;

“Next Generation Catalysts are turbulent: Development of Support and Coating”

SAE 2004-01-1488

[3] Kent Dawson, Ford; Jan Kramer, Emitec

“Faster is Better: The Effect of Internal Turbulence on DOC Efficiency”

SAE 2006-01-1525.

[4] Markus Downey, Klaus Müller-Haas, Emitec Inc.; Talus Park, Robert Diewald,

AVL Powertrain Engineering Inc.; Rod Radovanovic, Diesel Consulting

“Structured Foil Catalysts: A Road Map to Highly Effective, Compact

Aftertreatment Systems”

SAE 2007-01-4038.

[5] W. Maus, R. Brück, P. Hirth; Emitec GmbH; O. Deutschmann, N. Mladenov

”Grundlagen der laminaren und turbulenten Katalyse, Turbulent schlägt Laminar“

Universität Karlsruhe; 27. Internationales Wiener Motorensymposium,

Wien, 2006

[6] Scott Blanchet, Russell Richmond, Gerald Vaneman, Delphi

“Implementation of the Effectiveness-Ntu Methodology for Catalytic Converter

Design”

SAE 980673

[7] W.Maus, R.Brueck, P.Hirth, Emitec;

“SCR and particulate Aftertreatment systems for HD EU VI and NRMM Tier 4”

10. International symposium for automotive and engine technology,

Stuttgart 2010

[8] E. L. Cussler;

“Diffusion - Mass Transfer in Fluid Systems”

Cambridge University Press,

Cambridge/New York, 1997


[9] K.Althoefer, R.Brueck, W.Mueller, Emitec;

V.Ulmet, SWRI

“Innovative custom-designed catalyst concepts for LD and HD trucks”

FAD conference, Emission control for HD trucks,

Dresden 2006

[10] T.Nagel, J.Kramer, M.Presti, A.Schatz, Emitec

R.Salzman, J.Scaparo, A.Montalbano, Ford;

“A new approach of accelerated life testing for metallic catalytic converters”

SAE 2004-01-0595

[11] A.Karkkainen, B.Adelman, P.Berke, S.Wyatt, D.Rodgers, International Truck

and Engine Corporation

A.Heibel, T.Parker, D.Pickles, T.Tao, U.Zinc, Corning

“Development and Application of a US-EPA’07 Particulate Filter System for a

7.6L I-6 Medium Duty Truck Engine”

Aachen Colloquium 2006

[12] http://maxxforce.com/Application/truck-and-bus

[13] T.Seguelong, Aaqius&Aaqius,

“Performance and durability of PSA Peugeot Citroen’s DPF System on a Taxi

fleet in Paris”

DEER 2003, Newport, RI

[14] M.Khair, Southwest Research Institute

“A review of Diesel particulate Filter Technology”

SAE 200-01-2303

development and practical experience of … · a single engine family, such as the maxxforce® 7,...

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