CNG Fuelled Police Patrolboat

By Keith Henderson at May 03, 2012 09:00
Filed Under: Company News, Industry Events, Research & Development

The use of LNG as a fuel is growing in popularity for ships of different sizes and power to provide a solution to increasing fuel costs and reducing exhaust emissions. Using LNG requires storage not only under but also at low temperature. Cooling the gas into a liquid state at the low temperature of approximately -162 ̊C (-260 ̊F) allows it to be maintained at the low pressure of only 3.6 psi (0.25 bar). While cooling plant and well insulated tanks are feasible on a ship, on small vessels - boats, this is not practical. To access the benefits of natural gas operation, a more practical solution for boats is to use compressed natural gas (CNG). The drawback is that CNG is 2.4 times greater in volume than LNG.

In the Netherlands ten percent of automobiles run on LPG and a very small number of boats use is as a fuel, however its use in boats is regarded as being potentially dangerous as it is heavier than air and any escaping gas will accumulate in the bilges. Natural gas on the other hand is lighter than air and any escaping gas is lost to the atmosphere.

Caption: The CNG Water Police 18 ft RIB used to patrol the Netherlands inland waterways and canals.
Image Credit: K.Henderson

This year the Water Police that patrol the Netherlands inland waterways are experimenting with a dual fuel gasoline / CNG Honda outboard powered patrol boat. The boat is a 18 ft (5.6 m) Dolphin RIB powered by a Honda 90 VTEC outboard. In addition to the standard gasoline tank, there is a 24 US gall (90 liter) CNG tank with a capacity for 33 lbs (15 kg) of CNG, held under pressure of approx 3,000psi (~200 bar). The fuel system cold starts on gasoline and when operating temperature is reached switches over automatically to CNG and remains operating on gas under 2,000 rpm. Above that speed it switches over to gasoline to realise the full power of the engine.

In practical terms, the boat can patrol all day on one tank of CNG, when speed is required, it is always available and the performance of the boat is not impaired in any way due to the dual fuel capability. The fuel cost of CNG compared to gasoline in the Netherlands is about half, giving a substantial through life cost saving.

Caption: The 24 gall / 33 lbs CNG fuel tank mounted in the bilges.
(GROENGAS is Dutch for Green Gas!)
Image Credit: K.Henderson

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