Comments by "John Burns" (@johnburns4017) on "Engineering Explained"
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I was talking to a ship designer and they are always looking at ways of cutting running costs. Some were looking ahead and favoured rotary engines in banks in cruise ships if they were made large enough.
The 4 deck high Wartsila and Suzler engines when needing overhauling means the ship is dock, which means down time which costs. Ships and moreso cruise ship operators do as much maintenance as possible under way. They even paint the sides of the ship when in a calling port. They want the ship in dock only for essential dry dock maintenance like azipods, props or the keel. They want maintenance to be ongoing as the ship is moving and earning money.
Some ship's designers are looking ahead and favouring larger rotary engines in banks (slide out modules say 1.5 metre by 1.5 metre complete with generator) in cruise ships. Rotaries are one third of the size and weight for the same power output. The smoothness is a great asset in passenger accommodation. Rotaries scale up seamlessly.
The rotary genset modules can be phased in, in stages to what the ship's power demand is, rather than running these massive Sultzer engines when there is low demand. Then they can slide out a genset module in port and slide one in, which will take a few hours. The genset module in port can be overhauled onshore and the ship continues with no downtime maximising efficiencies and revenues.
The rotaries niche is where a constant speed is appropriate as in genset applications. Then the rotary overtakes the piston/crank engines in economy. Other niches are aircraft because of the superb power to weight ratio over piston/crank engines and UAVs currently exploit this well. Applications for ship gensets are way down the line and probably will only come about when there is a wider acceptance in vehicles, although large rotaries were commercially operational in the 1970s, Ingersoll Rand making the largest which reliably ran for many years.
As to ships, keeping the hull small enough to negotiate the Panama locks and packing as much cargo or passengers inside as possible increases the profitability. Replacing large engines with smaller lighter units which are flexible to the location inside the hull gives a ship designer great scope. More economical engines means smaller fuel tanks which again gives over more space for revenue earning cargo or passengers. Being secured in a strong niche market may elevate the rotary as the first choice of engine in time, as direct drive applications become rare.
Light weight rotary engines can be located out of the depths of the hull, instead of all laying on the keel. The flexibility of design is there. Many ships have Azipods for the the obvious manoeuvrability and also that they liberate space in the hull. Cruise ships want as much space as possible for revenue gaining. They cost a lot to run in crew and fuel costs. On the lower decks the crew are housed. Liberated engine space can accommodate more crew and lower the crew down maybe a deck or half a deck and utilise the liberated space for passenger functions, while moving these functions down decks will again liberate space on upper decks for more revenue earning passenger cabins.
The industry will move to smaller lighter engines if they are available for sure. They moved from steam to turbines and diesel piston engines. They move with the economic flow. Cruise ships use an amazing level of fuel, especially in hot climates when the a/c's are running. Size of propulsion and ancillary equipment in ships now matters. There have been large rotaries and they scale up seamlessly. A new large rotary in a genset would have the new innovations and improvement of over the past 40 years. Some newer rotaries are cooled through the driveshaft for instance giving engine longevity as hot spots are eliminated.
There is concern that vibration of ship's diesel engines could damage ancient historical buildings in places like Venice. Venetians constantly complain of this. Vibration is greatly eliminated using smooth rotaries. Having been on a number of cruise ships I can attest that vibration is a problem and I am always on around the 12th deck where it is minimal. What it is like further down I dread to know. I pity some of the crew near the engine room. Cabins on lower decks tend to be cheaper because of engine noise and vibrations; less revenue.
Look at the size, and weight, of a ship's diesel engine. It is massive taking up to 4 decks in height and cruisers have banks of these. The advantages of rotaries are easy to see.
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User Name wrote: ' It does best in constant rpm situations or high speed applications like a light weight sports car.'
The niche wankels are filling is range-extenders where the engine only turns a generator or UAVs where it is always running at high speed. They then are superior to piston engines. The small size, low weight and amazing smoothness will tip the scales. Mr Takashi Yamanouchi, the global CEO of Mazda stated, "The rotary engine has very good dynamic performance, but it's not so good on economy when you accelerate and decelerate. However, with a range extender you can use a rotary engine at a constant 2,000rpm, at its most efficient. It's compact, too."
+User Name wrote: 'The downside of the engine is its lack of reliability, the excessive use of oil, and the terrible emissions.'
Mazda are introducing the RX-Vision next year, which is direct drive, and claim to have solved the fuel and emissions problems. I do not doubt them. Use the engine as a range extender and it is bye, bye piston engine.
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