— 1 — © Wärtsilä Corporation, July 2004

German WeisserManager Engine Performance

Wärtsilä Switzerland Ltd, Winterthur

Fuel Saving with Sulzer RT-fl ex

As the fl exibility of the RT-fl ex common-rail system is explored in Sulzer low-speed engines, a new benefi t has been developed in terms of extending the choice in fuel consumption through Delta Tuning.

Choice in fuel consumption is not completely new. Since about 1980, Sulzer low-speed engines have been offered at ratings lower than the maximum continuous rating (now designated the R1 point) with benefi ts in lower fuel consumption. There was, of course, also the benefi t of improved propulsive effi ciency through the possibility of reduced propeller rotational speeds. This

concept led to the layout fi elds which we have used for some years.

It gave a choice but there were penalties in reduced engine power or alternatively a need for ‘more engine’ in terms of more cylinders or larger cylinder bore for the same power.

Now, with the Sulzer RT-fl ex common-rail engines, we are at the beginning of a new era in engine technology. This is encouraging new ways of thinking thereby leading to new concepts.

Whereas traditional camshaft-controlled engines were

Delta Tuning has been introduced in Sulzer RT-fl ex common-rail engines to provide lower fuel consumption in the effective operating load range. It is offered as an alternative to the original tuning thereby allowing ship owners and operators to choose the BSFC (brake specifi c fuel consumption) curve which best suits their ship’s operating pattern.

This is made possible by the tremendous fl exibility in engine settings provided by the computer-controlled common-rail systems of Sulzer RT-fl ex engines.

Fig. 1: The fi rst engine employing Delta Tuning

is this 45,760 kW Sulzer 8RT-fl ex96C engine

seen here in the course of erection at HSD Engine

Co Ltd, Korea.[04#027]

— 2 — © Wärtsilä Corporation, July 2004

Fig. 2: The new alternative BSFC curve for Sulzer RT-fl ex96C engines given by Delta Tuning compared with the original BSFC curves. All curves shown are for engines complying with the IMO NOX regulation.[04#102]

Fig. 3: The new alternative BSFC curve for Sulzer RT-fl ex58T-B engines given by Delta Tuning compared with the original BSFC curves. All curves shown are for engines complying with the IMO NOX regulation.[04#103]

severely restricted by the fi xed timing given mechanically by the cams, the change to electronically-controlled common-rail systems allows the timing, rate and pressure of fuel injection and the exhaust valve operation to be fully controllable. This fl exibility allows patterns of operation which cannot be achieved by purely mechanical systems.

Rather than ‘electronically controlled’, it would be more accurate to describe Sulzer RT-fl ex engines as being computer controlled. This is because in the RT-fl ex system, engine functions are fully programmable, perhaps limited only by the designers’ imagination and the laws of nature. The challenge is to use this freedom to create practical benefi ts for engine users.

The fi rst tangible benefi ts of the extreme fl exibility in engine setting possible with the RT-fl ex computer-controlled common-rail system are the engines’ greatly improved performance in smokeless operation at all loads, and its capability of running at very low speeds. Both have been reported in previous articles in “Marine News”.

Reduced BSFC

Now the fl exibility of the RT-fl ex system has been utilised to reduce fuel consumption in the effective operating range of most engines. At 75 per cent load, the fuel saving can be up to 2 g/kWh depending upon the engine model and the rating point selected. No changes

of hardware are involved, the development only requires changes in the RT-fl ex software to adjust the respective engine setting parameters.

At the fi rst stage of development of RT-fl ex engines, the main objective has been to obtain the same performance standards as with the mechanical-camshaft RTA-type engines, particularly with respect to power, speed, fuel consumption, exhaust emissions, cylinder pressures, etc.

It must be pointed out that RTA engines have always been highly competitive in fuel consumption right across the load range owing to the use of variable injection timing (VIT) and, in the case of the RTA84T engines since 1991, also of variable exhaust valve closing (VEC) which further reduces the part-load BSFC. These benefi ts have already been carried over to the computer-controlled common-rail systems of the RT-fl ex engines.

However, as combustion in the part-load range is better in RT-fl ex engines than with RTA engines, there is a quasi natural benefi t in fuel consumption for RT-fl ex engines at lower loads. This slightly lower BSFC at part load is the result of the fuel injection pressure being kept higher at those loads with the common-rail injection system.

The new step is to introduce a choice of fuel consumption curve. Two fuel consumption curves are now available as standard for RT-fl ex engines: the original one as outlined above and the new alternative, being a lower

-10

-8

-6

-4

-2

0

2

4

50% 75% 100%Load

RTA engines

RT-flex engines:

Standard tuning

Delta Tuning

∆BSFC, g/kWh

171 g/kWh

-6

-4

-2

0

2

4

6

50% 75% 100%Load

RTA engines

RT-flex engines:

Standard tuning

Delta Tuning

∆BSFC, g/kWh

170 g/kWh

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curve with reduced BSFC throughout the load range up to 90 per cent. It has been achieved by adapted engine tuning – termed Delta Tuning. In both the original tuning and Delta Tuning, the RT-fl ex engines comply with the NOX regulation of Annex VI of the MARPOL 73/78 convention, commonly referred to as the IMO NOX regulation.

Tuning technique

Delta Tuning involves tailoring the fi ring pressure to engine load through adapting injection timing, injection pressure and exhaust valve timing. The fi ring pressure is kept as high as possible at 75% load to observe a minimum required margin to the NOX limit, and is increased above 75% load to reach the maximum fi ring pressure at about 90% load. Then it is reduced again for higher loads. Below 75% load, the fi ring pressure is kept as high as is possible within the limit of the allowable fi ring ratio (fi ring pressure/compression pressure).

The result is that the BSFC is signifi cantly lowered in the mid- and low-load range, at all loads less than 90% load, but then increased at high engine loads (90–100% load). This emphasis on mid-load reductions in BSFC brings a real benefi t to engine users while allowing a higher BSFC at full load to enable the engines to comply with the IMO NOX regulation.

With the total fl exibility offered by the computer-controlled common-rail system, it would be technically possible to lower BSFC at all engine loads and speeds. With RT-fl ex engines, all the relevant parameters can be continuously varied so that the engine can – within the physical limits – follow any specifi ed BSFC curve as engine load and speed are varied. The two key limitations today, however, are in the needs to comply with the IMO NOX regulation and to ensure no diminishing of engine reliability and durability.

Owing to the natural laws of physics and chemistry, there is always a trade off between engine effi ciency and NOX emissions. Lowering the BSFC curve for an engine is almost inevitably associated with an increase in

NOX emissions and only the NOX emission penalty for achieving a certain BSFC reduction may vary between individual measures.

As the IMO NOX limit is specifi ed as a weighted average of NOX emissions measured at certain engine loads and speeds, the strategy with Delta Tuning is thus to accept increases in NOX emissions over a useful wide load range and to compensate with a reduction in NOX emissions at full load.

Two BSFC curves as alternatives

The result of Delta Tuning is a BSFC curve with a different emphasis than the original BSFC curve. Thus the two BSFC curves are offered as alternatives. They give ship owners and operators the opportunity to choose the BSFC curve which best suits their vessels’ operating pattern. Yet, in both cases, the engines comply with the IMO NOX regulation.

Delta Tuning, however, is only offered for Sulzer RT-fl ex engines whose contracted maximum continuous rating (CMCR) is in the upper region of the engine model’s rating fi eld, and it yields the greatest benefi t close to the R1 rating point. This is because there is a decreasing margin in NOX emissions against the IMO limit with greater derating.

The engine information for RT-fl ex engines with Delta Tuning will be readily obtainable using the ENSEL engine selection software and the WinGTD general technical data software which are freely available from the local Wärtsilä offi ces. In both cases, the software includes a selection button for Delta Tuning. Once Delta Tuning is selected, the software will restrict the engine layout fi eld to the area for which Delta Tuning gives worthwhile results.

Conclusion

Delta Tuning is a demonstration of the fl exibility of the computer-controlled common-rail systems incorporated in Sulzer RT-fl ex engines. It brings a clear benefi t to ship owners and operators, allowing them to choose how to adapt their engines better to individual operating requirements.