Strict new exhaust emission regulations, which came into force this January, have prompted big changes in the way tractor engines are designed. But how will they affect farmers? Mick Roberts finds the answers
Every other year, when the vast Agritechnica show comes around, we’ve come to expect a spate of new products.
But this year there’s even more activity than ever as manufacturers launch tractors and other self-propelled machines equipped with new engines to meet tough emission standard regulations introduced this January.
The new rules apply to all engines with power outputs between 174hp and 750hp, and cover tractors, combines, self-propelled foragers and sprayers.
With stocks of the previous engines now dwindling, most manufacturers are now introducing complete new ranges to comply with the legislation.
They are called Stage 3b in Europe and Tier 4 interim in the USA. Confusingly, manufacturers in the UK use one or the other and sometimes both titles.
The new rules force engine makers to reduce the soot in exhaust gas – known as particulate matter (PM) – by 91% and nitrogen oxides (NOx) by half, compared with the current levels.Amazingly, these levels of NOx and PM are now just 3% of those permitted in 1996.
However achieving these reductions has presented an enormous challenge to engine manufacturers.
The market has essentially polarised into using one of two design strategies, neither of which trips off the tongue. They are Selective Catalytic Reduction (SCR) or cooled Exhaust Gas Recirculation (EGR).
SCR uses high combustion temperatures to minimise particulate matter production. But this increases the levels of NOx, which it then deals with by treating the exhaust gases after they leave the engine.
To cut the NOx, a small amount of urea (3-7% of the diesel volume) dissolved in water (called AdBlue), is injected into the exhaust gas flow before being treated in a catalytic converter.
Some designs also employ something called a Diesel Oxidation Catalyst (DOC) to pre-clean the gas before it reaches the catalytic converter.
EGR uses cooler combustion temperatures, which reduces the NOx generated in the engine. This increases the levels of particulate matter, which are then physically filtered out of the exhaust gas.
It works by using a valve to divert some exhaust gas, usually from a variable geometry turbocharger, back into the combustion chamber. This depletes oxygen levels in the fresh air in the cylinders, which results in cooler combustion – cutting NOx production by about 50%.
Exhaust gas that is not recirculated first exits through a Diesel Oxidation Catalyst (DOC) which uses a catalyst to convert the hydrocarbons and carbon monoxide into water vapour and carbon dioxide.
The particulate matter content is captured by a Diesel Particulate Filter (DPF), which can cut emissions by the required 90% by essentially trapping the PM and oxidising them by burning.
It depends who you talk to. Tractor makers using SCR claim it is less complex than EGR and that it doesn’t require any extra cooling packages.
Also because it’s an after treatment, the engine can be set and optimised for performance and fuel economy at the same time. Tests do show better fuel economy compared with previous engines.
The main advantage of employing cooled EGR, claim its protagonists, is that it doesn’t require another liquid or delivery system and is a proven system in high load situations.
While the DPF does require periodic maintenance, there is no extra cost or inconvenience associated with having to source, store and fill another fluid.
SCR requires an extra tank and an AdBlue dosing system. Moreover, users need to not only purchase and put an extra liquid into an additional tank on the machine, they also need to store it carefully because it is sensitive to high and low temperatures and can deteriorate over the course of a year.
The EGR system probably involves more complex engineering and cooling the exhaust gases means more heat is produced, which in turn requires a larger exhaust gas cooler.
The particulate filter needs regular cleaning, but this is usually an automatic process which uses high exhaust temperatures (or an extra burner) to burn them off. Users don’t need to instigate this process and won’t even notice it’s happening.
Manufacturers are reluctant to quote an actual cost or even a percentage increase for the additional engine technology. But as everybody has to comply, the price rises should be roughly the same for all makes. EGR and SCR technology is said to cost about the same.
All manufacturers are, however, cushioning the blow by adding extra features on their new Stage 3b compliant machines. But to answer the question, expect to pay 8% to 12% more (at the very least).
Tractor makers employing SCR and EGR both claim fuel consumption savings on their Stage 3b-equipped machinery, as proven by the independent DLG organisation in Germany
|Model||SCR/EGR||Test Number||Specific fuel consumption (g/kwh*)||Adblue (%)||Adblue specific consumption (g/kwh)|
|Fendt Vario 828 Vario||SCR||11-0033||245||6.9||16.9|
|New Holland T7.270 Auto Command||SCR||10-268||261||4.6||12|
|John Deere 8335R PowerShift||EGR||profi 11/11||260||N/A||N/A|
* Specific fuel consumption (g/kWhr) is the quantity of fuel used to generate each kilowatt of power and allows the consumption of engines of different sizes/powers to be compared.
Yes, but you need to be quick. The rules apply to the engine, not the machine and manufacturers were allowed to hold stock engines to fit to equipment in production. But the unexpected rise in demand this year means these stocks are now running low – hence the rash of recent new launches.
John Deere, the main user of EGR systems on its tractors, says the Diesel Particulate Filter (DPF) working life depends on use, but is likely to need a thorough clean at 5,000-6,000 hours.
A similar interval is expected for the Diesel Oxidation Catalyst (DOC). Cleaning is a specialist job, so John Deere is planning to provide an exchange service for both the DPF and DOC. Cost will be about £800 for the pair.
Manufacturers that employ a DOC in the SCR system, however, say this and the catalytic converter are maintenance-free and should last the vehicle’s lifetime.
John Deere recommends the use of its Plus-50 II engine oil for its EGR-equipped engines, which permits a change interval of 500 hours.
A typical dealer price is £61.50 for 20 litres or £586.60 for a 205-litre barrel. If this is not used the oil change interval drops to 250 hours.Massey Ferguson, which uses SCR on its high power tractors, says the engine oil change interval is 400 hour or 500 hour, depending on range, using recommended oil meeting the API CJ-4/ACEA E9 standard.
A typical dealer cost for this is £66.57 for 20 litres or £555.06 for a 205-litre barrel.
Sorry, but there’s more to come. Stage IV/Tier 4 Final for the 175hp to 750hp power bracket comes into effect in 2014, reducing PM and NOx emissions to near-zero limits.
This requires an additional 80% cut in NOx from current levels. For engines generating powers from 75hp to 175hp the Stage 3b and Tier 4 Interim regulations come into effect in January 2012, followed by the Stage IV Tier 4 Final limits in January 2015. Emissions levels in this category, however, are less severe.
What is AdBlue?
AdBlue is a trade name for AUS32 – an aqueous urea solution of about 32.5% urea and 67.5% de-inonised and demineralised water. It is injected into the exhaust gases and, as it passes through a catalytic converter, it prompts a chemical reaction that converts nitrogen oxide (NOx) into nitrogen (N2), carbon dioxide (CO2) and water vapour.
How much does it cost?
Currently between 33-39p/litre, depending on quantity. October prices from a farm machinery dealer are: 33p/litre in 1,000 litre IBC; £120 for 210 litre drum; £12 for 10 litre container.
Where can I buy AdBlue?
It is widely available through fuel suppliers and machinery dealers as well as garage forecourts and service stations. The simplest and easiest answer will be to buy it from the dealer who supplied the machine.
Is AdBlue mixed in the fuel?
No, it’s held on the machine in a separate tank, usually next to, or integrated into the fuel tank with a separate, usually blue, filler cap. It is injected into the exhaust gases after combustion.
What about storage?
There are no statutory storage requirements for AdBlue and it does not need to be kept in a bunded store. However it has a typical shelf life of six months to a year, freezes at -11C and must not be kept at above 30C.
How much AdBlue does an engine consume?
About 3-6% of the diesel consumption, so about 1 litre of AdBlue for every engine hour. Independent tests (see above), however, show consumption of 4.6% and 6.9% AdBlue in tractors with SCR in tests (54-70 litres of AdBlue per 1,000 litres of diesel).
What happens if it runs out of AdBlue?
To comply with legislation, manufacturers must ensure the engine cannot run at full power without the SCR system operating. In practice a warning light and alarm sounds when the AdBlue levels are low.
If it runs out entirely there will be further warnings and the engine will de-rate progressively until it delivers half the power, although this procedure varies with different manufacturers. There is also an obligation to ensure the systems are tamper-proof.
AdBlue, stored in a separte tank on the machine, is injected into the flow of exhast gasses leaving the manifold. This mixture of gas and AdBlue then travels into the SCR catalyst where harmful NOx gases are converted to nitrogen and water.
Some manufacturers also add a Diesel Oxidation Catalyst (DOC) to pre-clean the gas it enters the catalytic converter.
EGR systems use a valve to divert some exhaust gas, usually from a variable geometry turbocharger, back into the combustion chamber. This depletes oxygen levels in the fresh air in the cylinders, which results in cooler combustion – cutting NOx production by about 50%.
Gas that is not recirculated exhausts through a Diesel Oxidation Catalyst (DOC) which converts hydrocarbons and carbon monoxide into water vapour and carbon dioxide.
Particulate matter content is captured by a Diesel Particulate Filter (DPF).