Martin J. Murtagh
and Timothy V. Johnson
Corning Incorporated – Corning, NY, US
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BSTRACTPrevailing global environmental concerns over mobile and stationary diesel emissions prompted strict legislation incrementally implemented over the first decade of the 21st century. The standards established by the new emissions legislation posed a significant materials science and engineering challenge. New requirements demanded greater efficiency from existing emissions after-treatment (catalyst support systems, i.e.
catalytic converters), as well as engine modifications. The challenge of acquiring means to meet the stricter standards generated the emergence of some innovative approaches. As a result, heavy and light duty diesel engine manufacturers (in North America, Europe and Japan) were faced with the challenge of implementing rapidly developing technologies to meet the environmental legislation for particulate matter (PM) and nitrogen mono and dioxide (NOx) emissions. Diesel particulate filters (DPF) are a critical component enabling modern diesel engines to meet these challenges.
The chapter will review the state of the DPF past, present and future, covering wall flow filter material choices, i.e. cordierite, silicon carbide, and aluminium titanate, and the wall flow DPF design considerations, such as component filtration (efficiency &
pressure drop), thermomechanical, and thermochemical properties derived from the fixed integration of both the macro and microstructural attributes.
Keywords: Diesel particulate filter; DPF; aluminium titanate; silicon carbide; cordierite;
particulate matter; oxide of nitrogen
Corning Incorporated – Corning, NY, USA; Email: [email protected].
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NTRODUCTIONRudolf Diesel, inventor of diesel engine in 1892, was a well-respected thermal engineer and a social theorist. Diesel conceived the diesel engine to enable independent craftsmen and artisans to compete with large industry, and by a fascination with the second law of thermodynamics, i.e. maximum efficiency of the Carnot cycle [1].
The motivation for the construct on the through-the-wall (wall-flow) Diesel Particulate Filter (DPF) is simply that diesel engines emit particulate matter (carbon, hydrocarbon, inorganic ash). Some 86 years after Diesel’s invention, GM patented the concept of the modern DPF in 1981 [2]. The DPF design is based on plugging an existing “honeycomb”
flow-through automotive catalytic converter in a “checkerboard” manifold design. That is, every other honeycomb cell was plugged on each end of the substrate with alternating patterns to create the wall-flow DPF. Corning Incorporated then developed the DPF in the early 1980’s under a royalty-free license from GM.
Diesel exhaust particulate matter (PM) is a regulatory concern [3] and the global diesel mobile emissions legislation (1994 to present) that was drafted secured the launch of the DPF as the critical element of the PM emission solution by 2006.
The global diesel mobile emissions legislation provided a significant material science and mechanical engineering challenge. It is common practice when discussing DPF's to identify the filter by the material description. In the early development of the DPF, the micro and macro geometry of the filter as well as the material, from which it is composed, played a substantial role in the filter survivability and filtration. While it was not disputed that the material properties play a major role in filter survivability, the filter geometry has an important influence upon temperatures reached during uncontrolled regeneration and thus upon survivability. If the filter was to provide the safety margin for uncontrolled regeneration with high soot loads, a high mass filter was required. If the system is to provide the safety margin, i.e. electronic control, by avoiding uncontrolled regenerations with moderate soot loads, a low mass filter became possible with and added through-the-wall pressure drop advantage. In either case, the filter requires good thermochemomechanical integrity.
This Chapter is a review of diesel particulate filters (DPF's) covering the legislation and regulatory history, filter material choice and geometry, and DPF with system design integration for application.
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EGULATIONSFigure 1 represents the diesel engine combustion tradeoff as a non-linear inverse relationship between PM and NOx. The emission legislation and regulations follow a vehicle year step down format of the PM and NOx criterion pollutants in gram per kilometer for the light duty diesel engines application and gram per kilowatt hour for the heavy duty diesel engine application. Shown in Table 1 is the United States Environmental Protection Agency (USEPA) overview of the regulated gross vehicle weight rating (GVWR) for light duty vehicles, light duty trucks, and heavy duty vehicles.
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Figure 1. Schematic of Particulate Matter (PM) as a function of NOx diesel combustion tradeoff.
Table 1. Overview of diesel vehicle classifications [4]
Diesel engines used in heavy-duty vehicles are further divided into service classes by GVWR:
Light heavy-duty diesel engines (LHDDE): 8,501 - 19,500, for use in HDV classes 2b - 5 Medium heavy-duty diesel engines (MHDDE): 19,501 - 33,000, for use in HDV classes 6-7Heavy heavy-duty diesel engines (including urban bus) (HHDDE): > 33,000, for use in HDV class 8
Figures 2 & 3 show the historical emission limits for light duty vehicles (LDV) in North America and Europe and heavy duty vehicles (HDV) in North America, Europe and Japan (ESC: European Steady State Cycle), respectively.
Vehicle Abbreviation Definition
Light-duty Vehicles (i.e. Passenger Cars) LDV maximum Gross Vehicle Weight Rating (GVWR) < 8,500 lbs.
Medium-duty Passenger Vehicles MDPV 8,501 - 10,000 lbs GVWR
Light-duty Trucks LDT Max 8500 lb GVWR, Max 6000 lb curb weight, and Max 45 ft^2 frontal area light light-duty trucks LDT1 Max 3750 lb LVW (loaded vehicle weight: curb weight + 300 lb) light light-duty trucks LDT2 Min 3750 lb LVW (loaded vehicle weight: curb weight + 300 lb)
heavy light-duty trucks LDT3 Max 5750 lb ALVW (adjusted loaded vehicle weight: avg of GVWR and curb weight) heavy light-duty trucks LDT4 Min 5750 lb ALVW (adjusted loaded vehicle weight: avg of GVWR and curb weight)
Heavy Duty Vechicles HDV 2b 8,501 - 10,000 lbs Heavy Duty Vechicles HDV 3 10,001 - 14,000 lbs Heavy Duty Vechicles HDV 4 14,001 - 16,000 lbs Heavy Duty Vechicles HDV 5 16,001 - 19,500 lbs Heavy Duty Vechicles HDV 6 19,501 - 26,000 lbs Heavy Duty Vechicles HDV 7 26,001 - 33,000 lbs Heavy Duty Vechicles HDV 8a 33,001 - 60,000 lbs Heavy Duty Vechicles HDV 8b >60,001 lbs
Heavy-duty Vehicles Passenger Vehicles
Light-duty Trucks
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Figure 2. Historical limits of the light duty vehicle diesel regulations PM as a function of NOX.
Figure 3. Historical limits of the heavy duty vehicle diesel regulations PM as a function of NOX (ESC:
European Steady State Cycle).