The Language of Advanced Diesel Technologies
The Science and the Lingo
New advanced diesel technologies have made your Grandfather’s diesel engines cleaner, quieter and more powerful than ever before. Some of these revolutionary innovations include:
· Closed Crankcase Ventilation
Closed crankcase filters are used to reduce emissions from crankcase breather tubes in most turbocharged after-cooled diesel engines by using a multi-stage filter designed to collect, coalesce, and return the emitted lube oil to the engine’s sump.
For MY 1994 to 2006 HD diesel engines, crankcase particulate matter (PM) emissions reductions provided by crankcase emission control technologies are about 25% of the tailpipe emission standards.
· Common Rail Fuel Injection
An advanced fuel pump technology that is part of the new fuel control system in clean diesel engines. By directly feeding the injectors from a single fuel pump, an electronic system can be incorporated that precisely controls the pressure and timing of fuel injection.
A more advanced and efficient common rail injection system is the Piezo Common Rail, which is currently being introduced in automotive applications.
· Diesel Oxidation Catalysts (DOCs)
Like catalytic converters already used on all new gasoline vehicles, diesel oxidation catalysts (DOCs) cause chemical reactions to reduce emissions without being consumed and without any moving parts.
o The catalysts reduce PM by as much as 50%, reduce visible smoke, and virtually eliminate the pungent odor of diesel exhaust.
o The catalysts can reduce the invisible gaseous ozone-forming hydrocarbons by more than 70% and carbon monoxide emissions by as much as 90%.
o DOCs have been equipped on over 250,000 off-road diesel engines worldwide for over 30 years and on over 1.5 million new HD highway trucks since 1994 in the US.
o DOCs can be installed on new vehicles or can be retrofitted on vehicles already in use.
o DOCs can be used not only with conventional diesel fuel, but have been shown effective with biodiesel and emulsified diesel fuels, ethanol/diesel blends and other alternative diesel fuels.
· Diesel Particulate Traps
A high efficiency diesel particulate trap removes PM in diesel exhaust by filtering exhaust from the engine. The filter systems can reduce PM emissions by 80 to greater than 90%.
· Electronic Controls
A computer controls mechanical switches that allow precise amounts of fuel to flow from the injector into the cylinder.
· Flow-Through Filters
Flow-through filter technology is a relatively new method of reducing diesel PM emissions that, unlike a high efficiency diesel particulates filter (DPF), does not physically “trap” and accumulate PM. Instead, exhaust flows through a catalyzed wire mesh or a sintered metal sheet that includes a torturous flow path, giving rise to turbulent flow conditions. Any particles that are not oxidized within the flow-through filter flow out with the rest of the exhaust.
To date, there has been limited commercial use of the flow-through filters but there is an increasing interest in this technology due to its ability to significantly reduce PM emissions from older, “dirtier” diesel engines.
Flow-through systems are capable of achieving PM reductions of about 30 to 70%.
· Glow Plugs
Typically comprises a heating coil in a metal tube closed at one end and filled with electrically insulating ceramic powder. These plugs help quickly start advanced engines.
· Improved Combustion Chamber Configuration
In an improved combustion chamber configuration, the cylinder head has been shaped to provide the proper space in which fuel/air mixture will ignite and burn most effectively, creating maximum power stroke.
· NOx Adsorbers
NOx adsorber technology is a catalyst technology for removing nitrogen oxides (NOx) in a lean (i.e., oxygen-rich) exhaust environment for both diesel and gasoline lean-burn direct-injection engines.
NOx adsorber technology has made significant progress and is currently being optimized for diesel engine emission control. Reductions in engine-out NOx emissions of as high as 90% have been demonstrated and it appears possible to develop the system into a functional and durable NOx control system for diesel exhaust.
· Selective Catalytic Reduction
Selective Catalytic Reduction (SCR) is one of the most cost-effective and fuel-efficient vehicle emissions control technologies available to reduce diesel engine emissions.
o Selective catalytic reduction (SCR) systems use a wash-coated or homogeneous extruded catalyst and a chemical reagent to convert NOx to molecular nitrogen and oxygen in the exhaust stream. In mobile source applications, an aqueous urea solution is usually the preferred reductant.
o As exhaust and reductant pass over the SCR catalyst, chemical reactions occur that reduce NOx emissions. SCR system can reduce NOx emissions by 75 to 90%, HC emissions by up to 80%, and PM emissions by 20 to 30%.
o SCR has been used on stationary sources since the 1980s and is beginning to find use in mobile source applications, including line-haul trucks, off-road equipment, marine vessels and locomotives.
· Turbocharging
Utilizes energy from the engine exhaust to boost performance. Exhaust gas drives a turbine wheel that turns a second turbine wheel in the intake air stream forcing more air into the cylinder reducing emissions and increasing performance.
· Ultra-Low Sulfur Fuel
Ultra-low sulfur diesel fuel is highly refined for clean, complete combustion and low emissions enabling the use of emissions treatment systems.
· Variable Injection Timing
An innovation in the new fuel control system. Electronically controlled high-pressure fuel injector releases the precise amount of fuel at the moment of maximum compression (when the piston reaches the top of the cylinder).
· Wall-Flow Diesel Particulate Filter
High efficiency filters are extremely effective in controlling the carbon fraction of the particulate, the portion that some health experts believe may be the PM component of the greatest concern.
Since the volume of particulate matter generated by a diesel engine is sufficient to fill up and plug a reasonably sized filter over time, some means of disposing of this trapped particulate must be provided. The most promising means of disposal is to burn or oxidize the particulate in the filter, thus regenerating, or cleansing, the filter. This is accomplished through the use of a catalyst placed either in front of the filter or applied directly on the filter, a fuel-borne catalyst, or burners that are used to oxidize or combust the collected particulate.
Low pressure exhaust gas recirculation (EGR) systems are used for retrofit applications in conjunction with high efficiency DPFs. In a low pressure EGR system, the recirculated exhaust is taken from downstream of the high efficiency DPF.
Around the world, more than 200,000 DPFs have been installed as retrofits and more than one million DPF-equipped cars have been sold in Europe. DPFs have also been used successfully on a variety of off-road engines since the mid-1980s.
Alkane thanks the Diesel Technology Forum and www.dieselforum.org for the research and information presented herein.
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