The aftertreatment challenge in the non-road market is making
the same system work and fit not just in one machine, but in
hundreds of different machines, some of which can be used for many
different purposes. This huge diversity of applications and the
relatively small unit numbers for each application, coupled with
the rapid introduction of new standards and the very high
performance needed from the engines and machines, requires a
sophisticated approach to product development. Furthermore, as
emissions requirements become ever more stringent, designing a
system to meet the legislation subject to packaging and cost
constraints becomes progressively more difficult. This is further
exacerbated by increasing system complexity, where more than one
technology may be required to control all the legislated pollutants
and/or an active control strategy is involved. Also a very high
degree of component integration is required. Therefore
aftertreatment system modeling is an extremely valuable tool in
aiding design of systems that can meet all these challenges.
Here the application of 1-dimensional numerical models, based on
chemical kinetics derived for real-world catalysts, for a vanadium
oxide ammonia selective catalytic reduction (SCR) de-NOX catalyst
and a PGM-based diesel oxidation catalyst (DOC) are described. Both
models have been developed with particular emphasis on the
simulation of emissions control performance for non-road
vehicles/engines over the highly transient Non-Road Transient Cycle
(NRTC).
These models have then been applied to investigate the
sensitivity of various design parameters on the performance of the
system. In particular, the effect of inlet NO₂/NOX, ammonia to
NOX ratio, minimum urea injection temperature and catalyst volume
on an SCR-only system and the effect of DOC volume and PGM loading
on a DOC + SCR system have been investigated. These are important
factors in the design of effective and flexible non-road emissions
control systems.