Transcript Northeast States CLEAN AIR ACADEMY

Advanced Mobile Source Training Course
MS 201 - Diesel
Session I. Motor Vehicle Diesel Fuel
b. Impacts of Diesel Fuel Properties
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
Overview
• Sulfur is the most significant and important property
in diesel fuel in terms of emissions impact far
exceeding other properties
• Other fuel properties have a relatively small impact
on emissions, i.e. distillation curve, aromatic HC
content, cetane number and viscosity
• Lubricating oil additives have a cumulative impact due
to inorganic metal ash compounds buildup
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
2
History of EPA Regulation of Diesel Fuel Properties
• Pre-1993 – 2500-ppm sulfur
• 1993 - < 500-ppm sulfur
• 2006 - <15-ppm sulfur
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
3
Sulfur is the Real Problem
• Combustion of fuel sulfur yields 95/5% SO2 /SO3
exhaust in direct correlation with fuel sulfur level
• These sulfur compounds adversely affect the
performance of all catalyst-based emission control
technologies
• Near zero fuel sulfur level is needed to maximize
emission control performance
• Fuel sulfur negatively affects engine life
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
4
Sulfur Impacts on Catalyst Technology
• Sulfur inhibition of catalyst performance
• Sulfur catalyst-site poisoning
• Chemical reactions of SO3 and sulfuric acid with
catalytic components forming unsuitable compounds
• Catalytic oxidation of SO2 to SO3 thus increasing
particulates
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
5
Fuel Sulfur Negatively Affects Catalytic
Emission Control Technology
•Sticks to Catalyst Sites (Chemisorption)
– Inhibits Gaseous Catalytic Reactions
– Long Chain Hydrocarbon Cracking Function Is Not Affected
•Catalytic Oxidation of SO2 to SO3
– Catalyst Increases this Reaction Under Exhaust Conditions
– SO3 Adds to Tailpipe PM Emissions – 40 to 50% of SO2 Can
Readily Be Oxidized to SO3. PM Emission Standards Can Be
Exceeded
•SO3 Reacts with Catalyst Base Metals to Form Metal Sulfates
Which Are Unsuitable or not Catalytic
Sulfur Is Not a Friend of Catalytic Emissions Control
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
6
Catalyst-Coated Filter DPF
Trapped Soot
Cell Plugs
Exhaust (CO2, H2O)
Out
Exhaust
(Soot, CO, HC)
Enter
Ceramic Wall with
Catalyst Layer
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
•MECA
7
The Magic of Catalysis is Interrupted
by Sulfur
• Catalytic Soot Filter - Small Crystallites of Precious Metal Are Dispersed
on High Surface Alumina and Base Metal Particles
This Is What Happens!
A.
….
….
….
….
….
….
….
….
……………………………….…...
……………………………….…...
……………………………….…...
……………………………….…...
….
….
….
….
….
….
….
….
….
….
….
HC,
CO,
NOx
….
….
….
….
….
….
PM
….
….
….
….
….
….
….
….
….
….
….
………………………………........
………………………………........
………………………………........
………………………………........
….
….
….
….
….
….
SO2
½ O2
Pt
Precious Metal
Crystallite
Porous Catalytic Layer
Integrated Within the
Filter Wall
Al2O3 Particle
SO3
SO2  SO3
% Conversion
Trange 200 to 600°C (O2 and T Dependent)
100
80
60
18 ppm SO2
40
O2 = 7%
20
0
400 500 600 700
Temperature °C
Precious Metal Sites Designed for Emission Control
Also Catalyze SO2 Oxidation
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
8
And Also This Is What Happens
B.
SO2
S
O2
Pt
Sulfur Sticks to Pt
Catalyst Site
Trange 200 to ~400°C
When Sulfur Sticks to the Catalyst Site, the
Preferred Emission Control Reactions Cease
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
9
And This Is What Does Not Happen
HC
CO
O2
Pt
CO2 +
H2O
NO
NO
O2
NO2
NO2
Pt
CO2 + NO
NO
C
AND
Although Fuel and Lube Oil HCs Are Still Cracked to Gaseous Forms –
Unimpeded by Sulfur
C5 to C10
SOF Type HC
Crack to
Gaseous HC
C15 to C45
Particles
Base Metal
Precious Metal
Catalyst
Surface
Well, at Least One Catalytic Function Is Not Impaired by SO2
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
10
Sulfur Impacts on Diesel Emission
Control Technologies
• Diesel Particulate Filter Systems
– NO + ½ O2  NO2 (inhibition or poisoning)
– O2  Oa + Oa ; and Ce2O3 + ½ O2   CeO2 (inhibition)
– SO2 + ½ O2  SO3 (form sulfuric acid and sulfate particulate)
Diesel Oxidation Catalyst
Forms sulfuric acid
Impeded HC and CO performance
Lean NOx Catalysts
Some LNCs are inhibited and others are tolerant depending
on catalyst composition
NOx Adsorbers
SO3 adsorb preventing NO2 adsorbtion
Requires periodic sulfate regeneration
SCR
SCR is fairly resistant but associated catalysts are not
NO + ½ O2  NO2 (inhibition or poisoning)
NH3 bypass catalyst inhibition
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
11
Other Sulfur Impacts on Diesel
Particulate Filter Systems
• Sulfate produced is a particulate and can exceed the
amount of carbon-based soot removed
• Sulfur fuel content above 15-ppm can result in Sulfate
produced exceeding the 2007 PM 0.01 g/bhp-hr
standard
• Compliance with ‘Not to Exceed’ requires <15-ppm S
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
12
Diesel Particulate Filter Filter Decreases Carbon PM
But Increases Sulfate PM
as a Direct Function of Fuel Sulfur Content
PM Components, OICA Cycle
Carbon and Other
H2SO4 7H2O
0.20
0.10
0%
CDPF
0.15
-122%
Engine-Out
PM Emissions (g/bhp hr)
0.25
0.05
74%
>95%
0.00
3
30
150
Fuel Sulfur Level (ppm)
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
Reference: DOE (DECSE - Report 4) [25]
350
•DECSE
13
PARTICULATE SULFATE vs FUEL SULFUR
Assumptions: BSFC = 0.355
H2O/SO4 = 7/1
0.0300
g(SO4+H2O)/bhp-hr
0.0250
0.0200
0.0150
0.0100
0.0050
0.0000
0
5
10
15
20
25
30
35
40
45
50
FUEL SULFUR, ppm
40% S CONV
50% S CONV
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
Reference: MECA
60% S CONV
CR-DPF
SwRI
CDPF
14
Other Sulfur Impacts on
NOx Adsorber Systems
• The NO oxidation catalyst also oxidizes SO2 to SO3
• SO3 reacts with the NO2 adsorbant to form a stable
sulfate
• Sulfate slowly moves toward saturation thus reducing
availability for NO2 adsorption
• The adsorbent must be regenerated by thermal
treatment >600oC to remove sulfur and restore
availability for NO2 adsorption
• Ultralow sulfur minimizes the cycle. Zero sulfur fuel
and lubricant is highly desirable
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
15
In The Case of the NOx Adsorber System
Sulfur Clogs up the Chemical Storage Media
SO2 + O2
CO2
SO3
Pt
Pt
BaCO3
BaSO4
NOx Trap
Gradually
Clogs with
Sulfate
Adsorption Mode: l>1
CO
HC H2
COS
H2S
SO2
Pt BaSO4
NO
NO2
Pt
Ba(NO3)2
BaCO3
Desulfurization Mode: l<1; T>600°C
Reference: FEV ref. [53]
Desulfurization: Less Frequent with Ultra-Low Sulfur Fuel
H2S Emission Is Objectionable
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
16
Sulfur Limit Selection was Influenced
by Several Factors
• The ‘lower the better’ for engine, air, emission control options,
and catalyst performance
• Clean fuel free from combustion acids is best for the engine
• Sulfate generation in the atmosphere is directly decreased
• NOx adsorber technology requires ultralow sulfur fuel
• Almost all catalyst functions are improved with ultralow sulfur
fuel
• Diesel ultrafine carbon-based particles and visible soot particulate
matter can not be reliably removed
• Health consequences required stringent emission standards for
particulate matter and NOx
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
17
Other Benefits of Ultralow Sulfur Diesel Fuel
• Initial estimates were for 4% reduction in fuel energy content
• Fuel economy estimate ranged from 2 to 4% reduction but
actual reports have found no loss and an expectation for
improvement
• Initial estimates of lubricity loss has not been realized. Organic
lubricity additives are added to overcome any potential loss
• Engine life is enhanced considerably and engine maintenance
reduced. The RIA for 2500 to <500-ppm S estimated a 30%
improved engine life based on two studies that respectively
predicted 40 and 50%. The RIA for <500 to <15-ppm
estimated an additional improvement
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
18
Other Fuel Properties
• Boiling Point / Distillation Curve
• Aromatic HC Content
• Cetane Number
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
19
Boiling Point / Distillation Curve
• This curve shows defines the temperature range at
which various components vaporize. T 90% or 95%
are important for diesel fuel
• Specification limits: T90 320 to 340oC; T95 340 to
370oC
• Lower T95 trends toward slightly lower engine out
particulates and higher NOx because of less high
density components
• Future specification direction toward T95 340oC
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
20
Aromatic HC Content
• Decreasing polyaromatic content from 8 to 1% can
slightly lower NOx and particulate
• There is a clear link to di- and tri-aromatic levels in
diesel fuel and PAH emissions
• Trend is to lower Total Aromatics from 25 to 15% and
Polyaromatics (di- + tri-) from 5 to 2%
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
21
Cetane Number, Index or Rating
• Diesel fuel must have a chemical structure that
facilitates auto-ignition
• Cetane rating is obtained by comparing compression
ratios required to obtain a 13o crank angle ignition
delay with a fuel under test and the reference mixture
• Higher cetane results in lower combustion noise but
no PM and little NOx impact
• Trend is to increase Cetane Number from 48 to 55
• Cetane improvers cannot contain ash
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
22
Impact of Diesel Engine Lubricants:
Sulfur
• Lubricant and additives contain sulfur, i.e. ZnDTP,
detergents, and some cetane additives
• Lubricant sulfur levels are typically 0.6% (6000-ppm)
• EPA estimated that lube oil consumption could
contribute the equivalent of 2 to 7-ppm diesel fuel
sulfur equivalent – a significant amount
• New low ash lube oils are entering the market with
1/3 sulfur contents by using lower S base-stocks and Sfree detergents
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
23
Lube Oil Phosphorous
• Source is Zinc-dialkyl-dithio-phosphate needed for
valve train lubricant – especially cam surfaces
• P accumulates on catalyst-based surfaces restricting
passage of gases to catalyst site and is also a catalystsite poison similar to but less severe than lead
• New lube oil formulations have 30 to 50% lower P
• Alternate formulations, including dithiorabanmates,
sulfurized esters, and olefins, are being investigated
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
24
Lubricating Oil Ash Compounds
• Lube Oil ash compounds are primarily calcium (Ca),
zinc (Zn) and phosphorous (P) [see previous slide]
• Ca is added to give the TBN (total base number) to
neutralize combustion acids. ULSD forms less acids
and TBN content can be lowered. Ca is also in
dispersants and detergents.
• Future lube oil Ca is expected to be reduced 40-50%
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
25
Redesigned Lubricant Formulations
• ASTM lube oil standard (PC-10) is being developed for
2007 Heavy Duty Diesel Engines expected to specify
lower sulfur and ash content
• ASTM lube oil standard (PC-11) is being considered for
2010 HDDEs may contain a P limit to protect
advanced NOx adsorber technology being developed
for the 2010 NOx standard
• European technology leading lubricant manufacturers
are marketing “LowSAPS” or “LowSPash” formulations
with lower S, P and ash additives matching the high
performance level of other lube oils
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
26
Go to: Projects/Academy
© 2005 Northeast States for Coordinated Air Use Management (NESCAUM)
27