Abstract
Next EU and USA exhaust emission legislations step (Stage IIIB / Tier 4i) for non road mobile machinery requires a huge abatement of PM emission combined to a moderate further decrease of NOx emission from tail pipe of Diesel engines.
The fulfilment of Phase IIIB / Tier 4i emission limits can be achieved by means of two main engine and exhaust after treatment schemes: EGR + DPF or SCR. Final legislations step (Stage 4 / Tier 4) will introduce a further strong abatement of NOx emission requiring EGR in combination with exhaust after treatment (EAT) for both NOx and PM emissions. More powerful cooling systems and sophisticate engine thermal management will be also needed to meet legislation requirements and to fulfil the needs of real life operating conditions.
The a.m. main technologies allow a large number of variants in terms of materials, layouts, regeneration schemes and operating media. The exhaust emission control technologies and thermal management above described will dramatically impact on the dimensions, costs, performance and layout of agricultural tractors, therefore the selection of the main technology scheme and the subsequent variants combination is of paramount importance in order to offer to the end user the bigger benefit in terms of overall vehicle performance with the minimum cost impact.
The present work shows a methodological approach to the development of a full range of agricultural tractors for Stage IIIB / Tier 4i which leads to the adoption of different main technologies or different variant combination depending on the tractor class. Such an engineering approach considers the statistical analysis of the vehicle mission profile, which defines which operations a certain tractor is used for and the time share of each operation during a year. Simplified Tier 4i engine models and/or preliminary results from predevelopment engine test are used to predict the engine impact on the vehicle and the tractor performance during relevant agricultural operations. Based on the results of such simulations the main technologies and their variants for engine and EAT have been selected for each tractor class.
Closed phase-in dates for different power classes and for different legislation stages, in conjunction with an extremely wide product portfolio, requires a reduction of the time to market. The authors presents advanced 3D Computational Fluid Dynamic simulations techniques to develop and virtually test cooling and thermal management systems.
Keywords: Diesel, Exhaust Emission, Agricultural Tractors, SCR, DPF