the system is due the euro 5 emission standard n not
power.
i would prefer inline vertical then horizontal engine
due to wear n tear during power strokes
The system is required to meet power output requirements AND to
improve emissions.
Engines without exhaust gas aftertreatment in the form of
Selective Catalytic Reduction (e.g. in the case of the MAN D 20)
often require quite significant de-tuning in order to comply with
emissions regulations. This means that in order to comply
with Euro 5 and EEV, a significant reduction of power and torque
(specifically at the low end of the engine speed range) is required
over and above what is required to meet Euro 2/3/4. A
reduction of power and torque in the cruicial low engine speed
range has a major impact on the driveability of a heavy vehicle
such as a city bus so to counter this issue, engine manufacturers
have improved fuel delivery systems and optimised turbocharging
(e.g. by the use of variable geometry turbochargers or multi-turbo
systems) so that in some cases, the final power and torque outputs
are equal, if not higher than that of equivalent Euro 3/4
engines.
As for the use of engines with horizonal vs vertical cylinders,
this is a matter of packaging constraints and operator
demand. Horizontal engines have been used for decades in
Europe, Australia, and elsewhere with extremely successful results
with no compromises.
