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  1. Join Date
    Oct 2002
    Posts
    457
    #1
    Auto Emissions Special Report: The Future of Clean Diesel

    21st Century Diesel: A Clean Future

    http://www.corning.com/environmental...9/article2.asp

    Consider the diesel engine: efficient, durable, economical, it moves more mass along roads throughout the world than any other technology for the money. And yet the diesel engine is coming under increasing criticism and pressure, in both the United States and elsewhere for its emissions.

    Under the US’s Tier 2 environmental regulations currently being proposed, for example, diesel engines will be held to the same standards as gasoline engines – a major challenge at the moment, given the stringent standards Tier 2 imposes. And emissions standards in Europe are becoming stricter as well.

    Some health groups are lobbying to have diesel exhaust declared a health risk. And there continues to be an image problem for diesel, particularly in the United States, where twenty-year-old memories of diesel automobiles in the 1970s bear little resemblance to the quiet, clean, high-performance diesels of today. Yet at the same time, tax incentives in Europe and the Corporate Average Fuel Economy (CAFE) requirements in the US make diesel highly attractive, particularly for large concerns looking to drive down fleet emissions averages.

    For all these reasons, diesel engine manufacturers and emissions-control companies are hard at work to perfect the diesel engine system of the 21st century: cleaner, faster, quieter, and technologically engineered to meet the most stringent requirements, under all operating conditions, with minimal cost to the consumer. There are three challenges any diesel solution has to meet: the control of nitrogen oxides, particulate matter, and toxic airborne contaminants (TACs).

    Diesel Graduates from the School of Hard NOx

    Nitrogen oxides present the most daunting ongoing challenge to the pursuit of lowering diesel emissions. Traditional three-way catalysts do not respond to the lean air-fuel mixture that makes diesel so efficient. Several technologies, however, are being introduced or are in development which address the NOx issue in lean-burn engines. Exhaust Gas Recirculation (EGR) reduces NOx 40% on average but even this is not enough to satisfy upcoming regulation. So what is the answer?

    Selective Catalytic Reduction

    One of the promising alternatives appears to be Selective Catalytic Reduction (SCR). SCR technologies use ammonia in the form of urea to supplement the catalytic reaction – in essence, giving nitrogen oxides the "extra" molecules needed to convert to harmless nitrogen and water.. SCR does not require special fuel, owing to its high sulfur tolerance, and can be a good candidate for retrofitting in heavy duty applications, since it does not necessarily require interaction with the engine controller. The technology has demonstrated a 70% to 90% NOx reduction in both the North American FTP cycle, and the New European Driving Cycle. And this demonstration has come not just in research labs, but through wide use in the later stages of development. In terms of efficiency and sulfur tolerance, SCR is a very promising technology.

    At the same time, SCR is not without its drawbacks. SCR produces relatively high N2O emissions compared to a conventional diesel engine. The urea form of ammonia it uses is not dispensed at every gas station, and would need to be: an immense undertaking in terms of capital investment and infrastructure development. And with urea use will come other demands within the automobile, such as an OBD system to monitor use, and precise control to avoid ammonia slip. Despite all these factors, SCR remains highly regarded as a NOx solution, at least in the heavy-duty sector.

    NOx Adsorber Catalysts

    NOx "traps" adsorb nitrogen oxides during lean cycles, and regenerate during periodic heat (and/or rich) spikes. To be effective, however, they require low-sulfur fuel to insure the durability of the catalyst materials – in gasoline applications, a maximum of 30 ppm for a 70% reduction, and 10 ppm for the peak 90% reduction which comes with heavier loading. Engine cycles must be adjusted so that periodic rich excursions will regenerate the filter, burning off NOx at 650º Celsius without producing significant amounts of smoke. For lean-burn gasoline engines, the NOx adsorber catalyst is currently the most promising emissions control technology, and some direct injection gasoline vehicles are already using these catalysts.

    In addition to their high efficiency, NOx adsorbers also have a number of other benefits, most deriving from their design simplicity. A relatively passive technology (other than requiring periodic rich excursions), NOx adsorbers or traps require no storage tanks or infrastructure costs. They are compact and efficient over the long life of the trap. And best of all, they are an extension of proven current technologies. However, their regeneration is dependent on highly sophisticated control strategies. If these are in place, and if the fuel sulfur issues in both Europe and the United States are resolved in favor of very low-sulfur fuel, NOx adsorbers may be the most promising route to NOx reduction.

    Non-Thermal Plasma

    One deNOx technology which many observers find promising is still in its experimental stage: non-thermal plasma. In this system, exhaust gases pass through a very intense field of charged particles. As a result, NOx and other particles dissociate and ionize into far more reactive particles, which can then be easily catalyzed downstream.

    Plasma technologies promise up to an 80% reduction, but so far this has been demonstrated only in laboratory environments – a far cry from the rigors of the road. Systems currently being tested are still too large and energy-consuming for practical use.

    Particulate Matter (PM) : A Fine Mess

    Of even greater concern than NOx to many health researchers is particulate matter (PM), the signature black soot many people still associate with diesel emissions. PM became a major emissions control issue in 1998, when the California Air Resources Board (CARB) declared PM a toxic air contaminant. CARB is considered to be in the worldwide vanguard of emissions regulation, and it became plain that the winds of change were blowing PM into the dustbin of history.

    Cleaning up most PM is a relatively simple matter, mechanically speaking. With the use of diesel particulate filters (DPFs), up to 99% of total particles by number can be trapped (see figure 4). At the same time, DPFs capture only 70 to 90% of particles by weight, due to an odd paradox: after having their tarry outer coating or soluble organic fraction (SOF) broken down by the heat of filter regeneration, the resulting gases reform as aerosols that show up as large particles coming out of the tailpipe.

    Most health specialists concerned about PM in ambient air are not as concerned with these larger particles, however. The bigger a particle, the less likely it is to be deposited deep into the lungs where it can do the most damage. Furthermore, most observers feel that with additional engine improvemetns, the SOF can be minimized.

    Still, new Tier 2 regulations emerging from the Environmental Protection Agency make it clear only very low levels of PM will be allowed in emissions from diesel passenger cars, light- and heavy-duty trucks. And while DPFs are compact, offer little in the way of back pressure (see related article), and represent a proven and inexpensive solution, many emissions engineers are concerned with developing reliable systems that burn off soot and regenerate themselves repeatedly over the life of the vehicle.

    Great strides have been made in this direction with the development of "common rail" engines featuring highly flexible combustion processes which allow for multiple injections to spike temperature as needed to regenerate the filter. As yet, however, regeneration often remains far less simple and efficient than emissions engineers would like. To address the problem, several different solutions have emerged.

    The Continuously Regenerating Trap (CRT)

    The CRT uses excess NOx to eliminate PM: NO is oxidized to NO2, which, in turn, oxidizes soot into carbon dioxide and nitrogen. The CRT system, however, requires a minimum NOx to PM ratio of 8:1 (which is generally available over most of the operating range) to work. The CRT can reduce PM by approximately 90% under optimal conditions – one of which is low-sulfur fuel (50 ppm or lower).

    Catalyzed Soot Filters

    These filters use a reactive catalyst to facilitate oxidation. At temperatures under 350° Celsius, they also can yield a 75% reduction in PM, and like the CRT, they are a passive method easily adapted to retrofitted engines.

    Catalyzed Fuel Additives

    Another school of thought involves putting catalysts directly into fuel. This answer is relatively inexpensive in terms of fuel-cost penalty, often adding up to only one or two cents a gallon, and offers 75+% efficiency (when used with filters). Some technologies utilize a system in which an additive is commingled into fuel from a supplementary reservoir next to the main fuel tank. The additive allows the particulate to burn (in a filter) at a lower temperature which common rail engine technology can easily reach through sophisticated combustion control.

    It should be noted that with all these technologies, the conversion efficiency for particles by mass is very much dependent on engine tuning. The smaller the SOF, the greater the efficiency. Active engine tuning, both "common rail" and otherwise, can go a long way toward addressing PM problems in both light- and heavy-duty vehicles.

  2. Join Date
    Oct 2002
    Posts
    457
    #2
    Toxic Air Contaminants

    While NOx and PM remain the biggest stumbling-blocks in clean diesel’s path to lower emissions, many observers feel that, ultimately, toxic air contaminants (TACs) will also be regulated, and should be addressed technically sooner rather than later. The US Environmental Protection Agency has listed formaldehyde in its Tier 2 regulation proposal, and many observers feel that other "toxics" such as Acetaldehyde, Acrolien, and Poly-Aeromatic Hydrocarbons PAHs will probably be regulated as well.

    There are over thirty different substances which the Environmental Protection Agency lizards as hazardous air pollutants. Although, at the moment, most of these toxic air contaminants are not regulated for mobile sources, a combination of worldwide health concerns, public interest, and the trend toward more stringent standards with each succeeding program suggests that they soon may be.

    Airborne TAC particles can be effectively dealt with by particulate filters. Traditional diesel oxidation catalysts have proven to be highly effective (up to 58%) in reducing TAC gases in diesel emissions (see figure 5), and with significant catalyst loading, the reduction rate can reach as high as 80%. To hit this high efficiency, however, the use of low-sulfur fuel will be necessary to ensure durability, due to the formation of sulfuric acid from oxidation catalysts.

    Clean Technologies/Clean Vehicles

    Diesel technology is at a turning point. Will diesel be refined with new tools to equip it for 21st century use, or will diesel be shunted aside, a thing of the past?

    The future of diesel is the immediate future: regulations in both Europe and the US are set to take effect as early as 2004, and clean-diesel emissions systems need to be developed to meet that timeframe. There are strong arguments to be made on behalf of diesel technology – its reliability, its economy, and not least of all, the fact that the retrofitting of existing diesel vehicles makes cleaning up diesel emissions much easier in the long run than introducing new, unproven technologies to highly diverse global markets.

    The choice is obvious. It only remains for the most creative, aggressive engineering to find the answers that will allow diesel to fulfill its great promise.

  3. Join Date
    Oct 2002
    Posts
    13,417
    #3
    haba! hehe... gusto ko padin ng mga Eurospec na TDi engines... Especially yung Opel Speedster na diesel :D

  4. Join Date
    Oct 2002
    Posts
    4,616
    #4
    wala nang future yung dream fully-mechanical diesels ng mga hardcore offroaders hehehe

  5. Join Date
    Oct 2002
    Posts
    10,606
    #5
    wala akong naintindihan. Parang si Mr. Spock at R2D2 naguusap hehehe! Beam me up scottie!

  6. Join Date
    Aug 2003
    Posts
    10
    #6
    can someone translate it to english?
    I thought all the while Diesel engines are more environment friendly than gasoline...
    bakit parang sa article na to, gas is better. alin po ba talaga?

  7. Join Date
    Oct 2004
    Posts
    665
    #7
    it isnt the engine that's the problem but the fuel quality. The fuel quality in the US is worse than what we have here. In the Tier 2 proposal they're gonna change there diesel quality from worse than Philippine diesel fuel to better than European diesel fuel. They can do this because they can afford and people in the US care about the environment.

    Dito sa Pinas it appears that gas is more environmentaly friendly than diesel.

    Quote Originally Posted by SrfsUp
    can someone translate it to english?
    I thought all the while Diesel engines are more environment friendly than gasoline...
    bakit parang sa article na to, gas is better. alin po ba talaga?

  8. Join Date
    Oct 2002
    Posts
    22,669
    #8
    Quote Originally Posted by mbt
    wala nang future yung dream fully-mechanical diesels ng mga hardcore offroaders hehehe
    Remember that there is a mantra in off-roading: "Built not Bought". Hehehe.

    Btw, diesels are more environment friendly to manufacture and a liter of diesel will go farther than a liter of gas when used in comparable engines.

    http://docotep.multiply.com/
    Need an Ambulance? We sell Zic Brand Oils and Lubricants. Please PM me.

  9. Join Date
    Aug 2006
    Posts
    47
    #9
    Quote Originally Posted by Dieseler View Post
    Toxic Air Contaminants

    While NOx and PM remain the biggest stumbling-blocks in clean diesel’s path to lower emissions, many observers feel that, ultimately, toxic air contaminants (TACs) will also be regulated, and should be addressed technically sooner rather than later. The US Environmental Protection Agency has listed formaldehyde in its Tier 2 regulation proposal, and many observers feel that other "toxics" such as Acetaldehyde, Acrolien, and Poly-Aeromatic Hydrocarbons PAHs will probably be regulated as well.

    There are over thirty different substances which the Environmental Protection Agency lizards as hazardous air pollutants. Although, at the moment, most of these toxic air contaminants are not regulated for mobile sources, a combination of worldwide health concerns, public interest, and the trend toward more stringent standards with each succeeding program suggests that they soon may be.

    Airborne TAC particles can be effectively dealt with by particulate filters. Traditional diesel oxidation catalysts have proven to be highly effective (up to 58%) in reducing TAC gases in diesel emissions (see figure 5), and with significant catalyst loading, the reduction rate can reach as high as 80%. To hit this high efficiency, however, the use of low-sulfur fuel will be necessary to ensure durability, due to the formation of sulfuric acid from oxidation catalysts.

    Clean Technologies/Clean Vehicles

    Diesel technology is at a turning point. Will diesel be refined with new tools to equip it for 21st century use, or will diesel be shunted aside, a thing of the past?

    The future of diesel is the immediate future: regulations in both Europe and the US are set to take effect as early as 2004, and clean-diesel emissions systems need to be developed to meet that timeframe. There are strong arguments to be made on behalf of diesel technology – its reliability, its economy, and not least of all, the fact that the retrofitting of existing diesel vehicles makes cleaning up diesel emissions much easier in the long run than introducing new, unproven technologies to highly diverse global markets.

    The choice is obvious. It only remains for the most creative, aggressive engineering to find the answers that will allow diesel to fulfill its great promise.
    sir ganda ng article mo. yes diesel is the way to go.i work for daimlerchrysler here in UK.we got our diesel engine both merc.and jeep are using the same diesel engine witch burns cleaner and with cat converter and oviously pass the euro emission requirement.yes they are very reliable not so noisy and the torque !they are good.the jag next door to us are having diesel also on theyre cars and you wont say its diesel more than 200 bhp from a 2.5 twin turbo engine.bimmer is having 330dc.coupe,how good is this even on a 2 door sport car , 300c,s80 .is powered by diesel.the only set back we're having is the parts are so expensive on those crd ,kahit na warranty prize it mimimum 379 pounds isa.the worst thing is pag nagkamali ng lagay ng fuel ang may ari recommended to change the whole fuel system.well anyway diesel is the way to go only less flexibility on fuel doesnt meant na di maco convert sa other fuel,lots of other country already has dual fuel. ty

  10. Join Date
    May 2006
    Posts
    6,905
    #10
    Bahala na PISTON at FEJODAP dyan. Sila na muna umintindi diyan bago tayo.

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Auto Emissions Special Report: The Future of Clean Diesel