© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) Advanced Mobile Source Training Course MS Diesel Session I. Motor Vehicle Diesel Fuel b. Impacts of Diesel Fuel Properties

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 2 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) 3 History of EPA Regulation of Diesel Fuel Properties Pre-1993 – 2500-ppm sulfur < 500-ppm sulfur <15-ppm sulfur

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 4 Sulfur is the Real Problem Combustion of fuel sulfur yields 95/5% SO 2 /SO 3 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) 5 Sulfur Impacts on Catalyst Technology Sulfur inhibition of catalyst performance Sulfur catalyst-site poisoning Chemical reactions of SO 3 and sulfuric acid with catalytic components forming unsuitable compounds Catalytic oxidation of SO 2 to SO 3 thus increasing particulates

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 6 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 SO 2 to SO 3 –Catalyst Increases this Reaction Under Exhaust Conditions –SO 3 Adds to Tailpipe PM Emissions – 40 to 50% of SO 2 Can Readily Be Oxidized to SO 3. PM Emission Standards Can Be Exceeded SO 3 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) 7 Catalyst-Coated Filter DPF Trapped Soot Cell Plugs Exhaust (Soot, CO, HC) Enter Ceramic Wall with Catalyst Layer Exhaust (CO 2, H 2 O) Out MECA

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 8 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. T range 200 to 600°C (O 2 and T Dependent) Pt SO 2 SO 3 ½ O 2 Precious Metal Crystallite Precious Metal Sites Designed for Emission Control Also Catalyze SO 2 Oxidation SO 2  SO 3 % Conversion Temperature °C 18 ppm SO 2 O 2 = 7% Al 2 O 3 Particle ……………………………….…... ……………………………… …. HC, CO, NOx PM Porous Catalytic Layer Integrated Within the Filter Wall

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 9 And Also This Is What Happens When Sulfur Sticks to the Catalyst Site, the Preferred Emission Control Reactions Cease B. T range 200 to ~400°C Pt SO 2 O2O2 S Sulfur Sticks to Pt Catalyst Site

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 10 And This Is What Does Not Happen Well, at Least One Catalytic Function Is Not Impaired by SO 2 Although Fuel and Lube Oil HCs Are Still Cracked to Gaseous Forms – Unimpeded by Sulfur SOF Type HC C 15 to C 45 Crack to C 5 to C 10 Gaseous HC Catalyst Surface Particles Base Metal Precious MetalPt CO O2O2 HC CO 2 + H2OH2O Pt NO NO 2 AND CO 2 + NO NO C C O2O2

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 11 Sulfur Impacts on Diesel Emission Control Technologies Diesel Particulate Filter Systems –NO + ½ O 2  NO 2 (inhibition or poisoning) –O 2  O a + O a ; and Ce 2 O 3 + ½ O 2   CeO 2 (inhibition) –SO 2 + ½ O 2  SO 3 (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 SO 3 adsorb preventing NO 2 adsorbtion Requires periodic sulfate regeneration SCR SCR is fairly resistant but associated catalysts are not NO + ½ O 2  NO 2 (inhibition or poisoning) NH 3 bypass catalyst inhibition

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 12 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) 13 Reference: DOE (DECSE - Report 4) [25] >95% PM Emissions (g/bhp  hr) Fuel Sulfur Level (ppm) CDPF Engine-Out % 0% -122% Carbon and OtherH 2 SO 4  7H 2 O PM Components, OICA Cycle Diesel Particulate Filter Filter Decreases Carbon PM But Increases Sulfate PM as a Direct Function of Fuel Sulfur Content DECSE

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 14 Assumptions: BSFC = H 2 O/SO 4 = 7/ FUEL SULFUR, ppm g(SO 4 +H 2 O)/bhp-hr 40% S CONV50% S CONV60% S CONVCR-DPFSwRI CDPF PARTICULATE SULFATE vs FUEL SULFUR Reference: MECA

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 15 Other Sulfur Impacts on NOx Adsorber Systems The NO oxidation catalyst also oxidizes SO 2 to SO 3 SO 3 reacts with the NO 2 adsorbant to form a stable sulfate Sulfate slowly moves toward saturation thus reducing availability for NO 2 adsorption The adsorbent must be regenerated by thermal treatment >600 o C to remove sulfur and restore availability for NO 2 adsorption Ultralow sulfur minimizes the cycle. Zero sulfur fuel and lubricant is highly desirable

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 16 In The Case of the NOx Adsorber System Sulfur Clogs up the Chemical Storage Media Desulfurization: Less Frequent with Ultra-Low Sulfur Fuel H 2 S Emission Is Objectionable Desulfurization: Less Frequent with Ultra-Low Sulfur Fuel H 2 S Emission Is Objectionable Reference: FEV ref. [53] Desulfurization Mode: 600°C NOx Trap Gradually Clogs with Sulfate SO 3 Pt SO 2 + O 2 CO 2 BaCO 3 Pt BaSO 4 Adsorption Mode: >1 COS H 2 S SO 2 Pt CO HC H 2 BaSO 4 Pt BaCO 3 NONO 2 Ba(NO 3 ) 2

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 17 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) 18 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) 19 Other Fuel Properties Boiling Point / Distillation Curve Aromatic HC Content Cetane Number

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 20 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: T to 340 o C; T to 370 o C Lower T 95 trends toward slightly lower engine out particulates and higher NOx because of less high density components Future specification direction toward T o C

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 21 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) 22 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 13 o 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) 23 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 S- free detergents

© 2005 Northeast States for Coordinated Air Use Management (NESCAUM) 24 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 catalyst- site 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) 25 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) 26 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) 27 Go to: Projects/Academy