Off-highway technology trends: strategies for Tier 4 Final / Stage 4 and beyond

This paper compares and contrasts the technology strategies for Tier 4 Final / Stage 4 off-highway emissions standards, focussing on the various combinations of EGR and SCR for NOx reduction. The importance of a low soot combustion system is emphasised as an enabler for low engine out NOx. In the case of higher EGR rates, very high injection pressures are shown to be beneficial.

The significance of the anticipated Stage V Particle Number (PN) limit is discussed. Results from a test programme with and without DPF, including the effect of very high injection pressures, are reviewed.

Legislation on Green House Gases or fuel consumption in the USA, Japan and other areas will soon be introduced for heavy duty, on-highway engines and vehicles. The resulting development of new technology for CO

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reduction for on-highway engines is reviewed and its potential impact on the off-highway engine market is considered.