In the models of high power tractors that begin to commercialize, the manufacturers emphasize that their motors are “Tier VIi - IIIB”. What is the difference in relation to the models that were replaced and what advantages do they offer?
With the publication of the Directive 2000/25/CE, it is established the obligation that the motors of the tractors and agricultural machines reduce their emission of greenhouse effect gases, establishing a calendar, according to which the maximum limits are lower and lower.
The established steps are designated like “euro”, “tier”, “stage” or “phase”, and in January 2011, for tractors over 175 CV of power, the stage IIIB/IVA came into effect, also well-known as tier IVi, in which the limit for emitted gases has been so reduced that we have been forced to introduce in the tractors new technologies, such as the injection of a solution of urea (AdBlue) in exhaust gases, to reduce nitrogen oxides, and to place a filter to retain the carbon particles that may reach the atmosphere.
In order to surpass the these limits, not all the manufacturers are using the same technology: some of them have chosen the injection of urea in the exhaust (System SCR - Selective Catalytic Reduction), while others do without the urea injection, and use the Exhaust Gas Recirculation (EGR) used in previous models, increasing the turbo-charging (with double turbo in series or with turbo of variable geometry) and also the pressure of injection in the common rail that reaches the 2000 bar. In both cases a particle filter has to be used, which cleans itself periodically, with different characteristics according to the used technology.
Both systems have advantages and disadvantages. For the SCR the highest disadvantage is the need to have an auxiliary tank with the AdBlue, equipped with a system of heating, and the volume of the set, that makes difficult to install them in small tractors; the advantage is that the motor can work with the Maxima efficiency.
Regarding the EGR motors, auxiliary tank is not needed, and the particle filter is smaller. Disadvantages: it needs a very high pressure injection system and it is necessary to cool and to filter the exhaust gases that go back to the motor. It is needed to specially take care of the quality of the diesel oil used.
In any case, the use of these systems means a continuing increase in the price of the tractor, which in principle it would be recovered with the reduction of the fuel consumption, but it is an imposition of the European regulation that any manufacturer who sells tractors in Europe must follow.