Methods of Meeting the New Emissions Requirements
Targeted emissions being reduced for diesel engines are nitrogen oxides (NOx), particulate matter (PM), non-methane hydrocarbons (NMHC), carbon monoxide, and sulfur.
Nitrogen Oxides (NOx) - nitrogen oxides are a contributor to ground level ozone formation (smog) and contribute to respiratory problems.
Particulate Matter (PM) - is small partials: organics, dust, and metals that make up soot seen in the engine exhaust on older diesel engines.
Non-methane hydrocarbons (NMHC) - various hydrocarbons are included in this group. NMHC contain compounds that are carcinogens and contributors to ground level smog.
Sulfur - sulfur present in diesel fuel contributes to the formation of sulfur dioxides. Like NOx, sulfur dioxide is also linked to respiratory problems.
Most of what I will be covering in this blog relates to the reduction of PM and NOx as the reduction of these two emissions has had the biggest impact on our diesel driven equipment. The reduction of sulfur is covered under fuel regulations (for example in the United States, diesel fuel is ULSD â€“ ultra low sulfur diesel), and the reduction of carbon monoxide and non-methane hydrocarbons doesn't have the same level of impact on our equipment. â€‹
WHAT IS IN-CYLINDER AND AFTERTREATMENT
The EPA does not mandate how engine manufactures reduce their emissions - what they do mandate is the maximum emissions in terms of g/kWh the engine generates. There are two methods to reduce emissions - in-cylinder or using aftertreatment.
In-cylinder - works by preventing PM or NOx from forming by changing the fuel injection rate and method, cylinder temperature and pressure, and/or varying oxygen concentration in the cylinders.
Aftertreatment - works by treating the exhaust coming out of the cylinders to remove NOx or PM before the exhaust is vented to the atmosphere.
Engine manufacturers use both in-cylinder and aftertreatment to meet emissions requirements.
WHY IT'S SO HARD TO REDUCE PM AND NOX
Reducing PM and NOx is an inverse relationship. So as the NOx levels in the exhaust are decreased, the PM levels are increased. Likewise, as PM levels are decreased, the NOx Âlevels are increased. For this reason, multiple techniques are required to meet the required levels of PM and NOx.
Some of the technologies used in the diesel engines you will see on Godwin's new final Tier 4 diesel equipment are Exhaust Gas Recirculation (EGR), Diesel Oxidative Catalyst (DOC), Selective Catalytic Reduction (SCR), and Diesel Particulate Filters (DPF).
EXHAUST GAS RECIRCULATION (EGR)
At Xylem, we started seeing exhaust gas recirculation in Tier 3 engines. EGR is used to reduce NOx emissions. In EGR, a small portion of the exhaust stream is recycled back into the cylinder inlet. Air in the exhaust has a lower oxygen content due to some of the oxygen being consumed in the combustion process, and this recycled air dilutes the oxygen concentration in the incoming ambient. Less oxygen in the cylinders means less NOx is formed. EGR is considered an in-cylinder method of treatment.
DIESEL OXIDATIVE CATALYST (DOC)
A diesel oxidative catalyst is a catalytic converter that is installed on the exhaust stream and reduces NMHC. Similar to the catalytic converter used in automobiles, DOC is present in many final Tier 4 engine models. Examples of Xylem equipment with DOC include the CD103M with a final Tier 4 Isuzu engine and a CD150M with a final Tier 4 John Deere 4045TFC03.
SELECTIVE CATALYTIC REDUCTION (SCR)
Like DOC, SCR is a catalyst but SCR is used to reduce NOx in the exhaust stream. SCR also requires an additional reactant - ammonia. Diesel exhaust fluid (DEF) is used as the source of ammonia. DEF is made up of roughly a 70/30 mixture of water and urea. DEF is introduced into the exhaust stream upstream of the SCR and reacts with the NOx in the catalyst.
At Xylem, all final Tier 4 diesel pumps with engines larger than 75hp (CD225M, HL100M, and larger) will have SCR. Diesel pumps with final Tier 4 engines below 75hp (CD150M, HL80M, and smaller) have slightly less stringent requirements for ÂNOxÂ emissions and do not have SCR.
DIESEL PARTICULATE FILTER
The diesel particulate filters (DPF) physically capture the soot (PM) coming out the exhaust in small pores. This soot builds up and needs to be removed, which is done using a process called regeneration. During regeneration, soot built up in the DPF is burnt off by raising the temperature in the DPF.
At Xylem, we have found operating engines with DPF challenging in pumping applications. In order to regenerate, DPF's must be heated to a specific temperature. If the DPF can't reach that temperature for some reason, (ambient temperature is too low, engine speed too low, not enough load on the engine) the engine will continue to build soot in the DPF until it reaches a shutdown point. At that time, a mechanic will be required to do a service regeneration on the engine.
John Deere, Caterpillar and Yanmar are all using DPF on most of their final Tier 4 engines. Xylem has had great success with these manufactures in the past and is still going to offer these engines, but due to the increased cost and complexity of engines using DPF, we are also offering final Tier 4 engines that do not use DPF. For this reason, Xylem now offers diesel driven pumps with JCB, Volvo, and Isuzu engines which do not use DPF, are much simpler to operate, and significantly less expensive.
WHAT DOES THIS MEAN FOR ME?
Xylem is in a somewhat unique position as an OEM in that we manufacture and rent equipment, so we have the ability to test these engines both in a factory setting and in applications. So whichever way you choose to go with your diesel driven pump, we have final Tier 4 powered pumps in our rental fleet and we stock parts and operate them on a daily basis. We are ready to help you with your new pump!
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