Texaco Delo 600 ADF – reducing diesel emissions in construction and agriculture
- Diesel emissions legislation focuses on plant and machinery
- Engines need external exhaust PM filters to meet new limits
- PM filter regeneration an operational and economic issue
With clean Euro VI vehicles dominating European truck fleets, the emphasis on reducing diesel emissions is now switching to other sources, including construction and agricultural machines. These industries are now coming to terms with technologies including exhaust gas recirculation (EGR), Selective Catalytic Reduction (SCR) and Particulate Filters (PM filters), in addition to common-rail injection and full electronic engine control. In doing so they are following in the footsteps of the transport industry and are encountering many of the same issues.
Exhaust emissions from NRMM engines have been regulated since 1999, in a staged approach. Regulated exhaust pollutants included carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and particulate matter (PM) from the outset. Like the Euro emissions for heavy commercial vehicles, these are measured in terms of grammes produced per kilowatt/hour of engine power output, with ammonia output being added at Stage III/IV, which was phased in from 2006 to 2013. The particulate limit was tightened at Stage IIIB, in a move intended to ensure that all diesel engines were fitted with PM filters, but the reality was that some designs conformed to the new requirement by using in-cylinder technology to improve combustion rather than an aftertreatment to clean unburned carbon particles from the exhaust stream.
Stage IV saw a steep reduction in allowable NOx, which encouraged many manufacturers to install SCR systems and add AdBlue tanks to their engines. This is the current standard and is seen as being broadly equivalent to Euro IV in commercial vehicles, which is when the use of SCR and/or EGR and PM filters became standard across the transport industry.
Stages I, II, and IIIA were tested with the engine running in a ‘steady-state’, but since then a more realistic transient test cycle has been introduced, with the engine running at a variety of loads, and with a cold-start included. So-called ‘defeat devices’ and ‘irrational control strategies’ (which have notoriously been used to ‘game’ emissions tests in the automotive sector) are specifically prohibited.
Industry is now poised on the brink of NRMM Stage V emissions limits. These include a drastic tightening of particulate output, to ensure highly-effective technologies such as wall-flow filters are used. Due for introduction in June and December 2020, depending upon engine size, these limits have now been postponed for 12 months in response to the Covid crisis.
The delay gives manufacturers a chance to clear stocks of new machinery that would have been sold before the deadline in normal times. Introducing sophisticated emissions control measures to arduous applications such as agriculture and construction has not been problem-free. Issues such as fuel cleanliness and the availability of AdBlue at remote locations have posed challenges for operators who had previously been used to operating machines that were designed to cope with adverse conditions. Likewise, the old practices of using one oil for all applications in all machines (for instance, the old Tractor Oil Universal which did duty in everything from the hydraulics and brakes to the engine) is not acceptable in modern machines. One reason for this being the need for a Medium or Low SAPS engine oil to avoid clogging the particulate filter with ash.
In agriculture, tractors and other machines fitted with particulate filters need to undergo an ‘hot’ active regeneration at regular intervals: 500 operating hours being typical. Additional fuel is injected and burned, either into the engine’s cylinders post-combustion or via an additional injector in the exhaust system. This entails taking the machine out of service for around 45 minutes, and care must be taken as to where and when the operation is undertaken. A regen in a dry harvest field could have catastrophic consequences, so operators tend to schedule it with a visit to the workshop for an oil service.
By all accounts, construction machines are less predictable than their farming counterparts. An industry source tells us: “The regen schedule is set by the manufacturer, but actual operating conditions can vary widely when compared to the factory test cycle. The machines operate in all kinds of environments, indoors and out, and seasonality also has an influence.
“For example, in Winter, drivers may leave machines idling for long periods to warm the cab. In those circumstances, the filters seem to need more frequent active regeneration than they do in Summer. Unexpected regenerations can also cause operational problems. If a machine is working in a waste transfer station for example, it is in an indoor situation, and surrounded by flammable materials. It has to be moved to a safe location before the process is initiated. Even if working outside, it is likely to have people and other machines in proximity so a clear area must be found.”
The situation is worse if the machine is on ‘dry hire’…hired out without a driver.“You are out of control of the situation once you have left the machine,” our source explains. “You can explain things all you like, but ultimately you are trusting the hirer to take note of warnings and seek advice. If the machine shuts down because warnings have been ignored, then you are faced with the cost of getting a replacement onto site, and removing the first machine for attention.
“Even though the fault may have been caused by operator error on the part of the hirer, recovering the additional cost can cause bad feeling and may lead to the loss of a customer, so in some cases you just have to take it on the nose.”
For machine operators in all sectors, the fuel burn required to regenerate filters represents an additional cost. This cost can rise drastically if the wrong engine oils are used: if the exhaust has a particulate filter then an oil which is not to the required specification (Low or Medium SAPS), then the filter will clog prematurely with ash. This material is untouched by the regenerative process.
The reduced filter capacity initially increases the required frequency of regenerative burns, but ultimately the ash will fill the filter to the extent that it needs to either be removed for specialist cleaning, or replaced with a new component.
