WITH tier 1 and 2 engine emission regulations now in force, engineers are turning their attention to developing engines which can comply with more stringent and demanding Tier 3 and Tier 4 requirements.

The first Tier 3 engines, depending on horsepower, are required to be in use by 2006, but John Deere, like most other engine makers, plans to introduce models before that date.

April will see Deere start production of a 6.8-litre Tier 3 compliant engine, which will be used initally for non-agricultural applications.  The firm’s 6000-series tractors will eventually use a version of this power plant. A 9-litre engine is currently under development for larger machines.

Both will use an exhaust gas recirculation system to achieve the required emissions levels of nitrous oxide – NOx – and hydrocarbons.

This will be the first time a repeat gas flow system has been used in engines for agriculture.

The thinking behind it is that when exhaust gases are burnt twice, emissions fall to the required levels. So, some of the exhaust is diverted back into the flow of air entering the

The rest of the exhaust is used to power the turbocharger, which boosts airflow into the engine.

While it may appear that only some is returned for reburning, after the initial start up, all of it is reburnt.

A turbocharger control varies the percentage of exhaust diverted back into the engine. It is cooled by a heat exchanger before it is mixed with incoming air leaving the intercooler.

Clearly, this is dependent on some sophisticated electronic control – exhaust gas ratios, gas temperatures, incoming air volumes and more – in addition to a workload which already includes organising injection timing and fuel volumes.

But there is a cost to all this, and not just to cover the extra development and build costs. Ironic as it may appear, an engine designed to cut emission levels actually needs to burn more fuel to achieve it.

Despite having cracked the problems of complying with Tier 3, Tier 4 – to be phased in from 2011 – looks daunting. How it will be achieved is unclear, but one detail has been agreed on: Fuel sulphur will have to be cut to allow sulphur sensitive control systems such as catalytic particulate filters and NOx absorbers to work.

Sulphur levels will need to fall from an average of about 3000ppm to just 10ppm. 

An advanced exhaust gas after-treatment system may also need to be developed.