The Miller cycle is a modification of the four-stroke cycle in which the inlet valve is closed earlier (or later) than normal so that the effective compression stroke is shorter than the expansion stroke. In the "early inlet valve closing" (EIVC) version, the inlet valve is closed well before BDC, so the air charge is expanded and cooled during the remainder of the downward stroke; the effective compression ratio is lower than the expansion ratio. In the "late inlet valve closing" (LIVC) version, the inlet valve is held open past BDC so some air is pushed back into the inlet manifold, again reducing the effective compression ratio. The result is that the charge air temperature at the end of compression is lower than in a normal cycle. Because NOx formation is strongly dependent on the peak combustion (flame) temperature, the lower compression temperature reduces the peak combustion temperature and hence reduces thermal NOx formation. The Miller cycle therefore lowers NOx without the fuel penalty of retarding injection, and is a primary internal engine measure for Tier II/III compliance. The engine must be turbocharged to compensate for the reduced air mass (higher boost) to maintain power.

1. Inlet valve timing: the camshaft/cam profile (or the electronic valve control) must be modified to close the inlet valve early (or late) - a new cam profile or a variable valve timing system.
2. Higher turbocharging/boost: because the effective compression ratio is reduced, the engine needs a higher charge-air pressure (higher turbocharger pressure ratio) to maintain the same trapped air mass and power; this may require a larger or two-stage turbocharger, and a charge-air cooler to keep the air temperature low.
3. Charge air cooling: an efficient charge-air cooler is needed to keep the compressed air temperature low (the Miller effect relies on low charge temperature).
4. Combustion chamber/injection: the injection timing and possibly the compression ratio may be adjusted to maintain good combustion and Pmax; the piston/cylinder head may be modified to suit the lower effective compression.
5. Valve gear/actuation: the valve train must be able to close the inlet valve at the required early/late angle reliably (stronger springs or hydraulic/electronic actuation).
6. Control system: the engine management must be updated to set the correct valve timing and injection for the Miller operation, and to protect against the higher boost and lower compression.

Open-loop scrubber: uses sea water as the scrubbing medium; the sea water is sprayed into the exhaust, absorbing SOx, and the wash water (now acidic) is discharged overboard after treatment. Advantages: simple, low cost, no chemical storage, high SOx removal. Disadvantages: cannot be used in enclosed/port waters where discharge of acidic wash water is restricted; consumes large quantities of sea water; the acidic discharge must be monitored and may be limited by regulations; not suitable in low-alkalinity sea water.

Closed-loop scrubber: uses fresh water with an alkaline additive (e.g. caustic soda/NaOH) as the scrubbing medium, which is recirculated; the SOx is neutralised and the wash water is treated and either discharged (after treatment) or stored. Advantages: can be used in port/ECA waters where open-loop discharge is banned; much less water used; the discharge is treated to meet limits; independent of sea-water alkalinity. Disadvantages: more complex, higher cost, needs storage and handling of the alkaline chemical (NaOH), produces a sludge/waste stream that must be disposed of, and higher operating cost.