THERMODYNAMIC ANALYSIS OFALTERNATIVE MARINE FUELS FOR

MARINE GAS TURINE POWER PLANTS

COMMONLY USED MARINE FUELS

Marine Diesel Oil (MDO) Residual Fuel Oil (heavy fuel oil) Intermediate Fuel Oil (MDO + HFO) Low Sulphur Marine Gas Oil (MDO+low

sulfur diesel )

EMISSION REGULATIONS MARPOL Convention treaty Maximum sulfur content in fuel used on

onboard ships – 3.5% as of january 2012

By 2020 sulfur content should not exceed 0.5%

WHY ALTERNATIVE MARINE FUELS High Cost of installation,operation and

maintenance of NOx and SOx reduction treatment device

High Cost of low sulfur fuels Need of dual fossil fuel systems

ALTERNATIVE MARINE FUELS Natural Gas Propane Hydrogen

Fuel Symbol Calorific value /(kJ·kg−1)

Stoichiometric air fuel ratio

Max. excess air factor

Diesel C12H26 42 800 15.14 3.11

 

Natural gas CH4 50 000 17.39 3.13

 

Hydrogen H2 120 000 34.78 4.03

 

PROPERTIES OF DIESEL, NATURAL GAS, AND HYDROGEN FUELS

MARINE GAS TURBINE ENGINES

COMPARISON OF GAS TURBINE PERFORMANCE PARAMETERS USING ALTERNATIVE FUELS

Comparison of gas turbine performance using diesel, natural gas, and hydrogen fuels was made assuming constant power output.

Comparison is based on LM2500 MARINE GAS TURBINE MODEL

CYCLE EFFICIENCY The gas turbine performance is limited

by the predominating ambient temperature of inlet air

Power output is inversely proportional to the ambient temperature of inlet air

Study determined that both gaseous fuels provide a lower efficiency than the original case of diesel for the same power output

CYCLE EFFICIENCY OF DIFFERENT FUELS

SPECIFIC FUEL CONSUMPTION The higher calorific value of both natural

gas and hydrogen compared to that of diesel reduces the quantity of fuel required to give the same heat output

Specific fuel consumption for natural gas and hydrogen is lower than that of diesel

Advantage could not be realised because of the lower density of these two fuels compared to diesel

Specific fuel consumption comparison as a function of

inlet air temperature for different fuels

SPECIFIC FUEL CONSUMPTION COMPARISON AS A FUNCTION OF COMPRESSION RATIO FOR

DIFFERENT FUELS

Specific fuel consumption of the three fuels increases with an increase in the inlet air temperature

The fuel consumption rates decrease with an increase in the compression ratio.

PEAK TEMPERATURE

Hydrogen and natural gas were controlled to avoid obtaining higher combustion temperatures than diesel to avoid increase in turbine blade cooling

Peak temperatures obtained for the natural gas and hydrogen are lower than that obtained for diesel

Comparison of maximum cycle temperatures for various fuels at different inlet air

temperatures

Comparison of maximum cycle temperatures for various fuels at different compression ratios

EXHAUST TEMPERATURE

main parameters affecting gas turbine exhaust temperatures are inlet air temperature and the compression ratio

The temperature of exhaust gases increases with an increase in the inlet air temperature

the exhaust gas temperature decreases as the compression ratio increases in relation to increased rates of inlet air mass flow

Exhaust temperatures as a function of inlet air temperature: comparison of different fuels

Exhaust temperatures as a function of compression ratio: comparison of different fuels

WORK RATIO The work ratio is the ratio between the

useful work developed inside the engine and the total work developed

Due to the lower efficiency of gaseous fuels, the work ratio of the fuels also appears inferior to that of diesel

The work ratio decreases in line with an increase in the compression ratio for the three fuels

Work ratio as a function of inlet air temperature: comparison of different fuels

Work ratio as a function of compression ratio: comparison of different fuels

The compressor inlet temperature and the intake air density dictate the mechanical work required by the compression process

The quantity of fuel used in obtaining the necessary temperature at the gas turbine inlet

AIR MASS FLOW RATE The gas turbine output power is directly

proportional and limited by the air mass flow rate

The mass flow rate of air is dependent on the temperature and relative humidity of the ambient air

The air flow rates for natural gas and hydrogen fuels are higher than that of diesel, because of the higher stoichiometric air to fuel ratio for gaseous fuels than that of diesel fuel

In gaseous fuel engines a greater amount of air is used to keep the temperature in a reasonable range, and thus part of the heat generated by fuel combustion is lost to enable a decrease in maximum temperature.

Air flow rates versus inlet air temperature for different fuels

Exhaust mass flow rate

For natural gas and hydrogen, the exhaust mass flow rate is also increased, although by a smaller percentage compared to the diesel

This smaller increase is due to the lower fuel flow rates for both the gaseous fuels

Exhaust flow rates versus inlet air temperature for different fuels

EXHAUST FLOW RATES VERSUS COMPRESSION RATIO FOR

DIFFERENT FUELS

This study shown that gaseous fuels

deliver a good performance compared to diesel fuel, and that natural gas is the currently the best choice of hydrocarbon to replace diesel fuel as it can be supplied at a relatively low price and is highly availabile

why alternative is better liquid fuels, which are currently used with

marine gas turbines, are associated with a number of environmental and economic issues

natural gas and hydrogen fuels can overcoming the difficulties associated with current marine liquid fuels.

the thermodynamic performance of natural gas is found to be close to that of diesel oil, and its maximum cycle temperature is 1474 K, which is close to that of diesel fuel (1485 K).

gas turbine thermal efficiency was found to be 1% less in the case of hydrogen compared to diesel, with a maximum cycle temperature of 1445 k

gaseous fuels deliver good performances compared to diesel fuel, but to achieve such performances the engine compressor and turbines need to be modified to accommodate differing flow rates

fossil fuel reserves will ultimately be exhausted, particularly with the increasing global energy demand

hydrogen could eventually be introduced to replace fossil fuels once the problems associated with its application are solved, such as the cost of its production and its storage onboard vessels.

hydrogen fuel could be considered as an alternative new fuel for marine gas turbines in the long term, but in the short term natural gas represents a positive solution for marine applications.

REFERENCE Aviation GE, 2015. LM2500 datasheet.

General Electric.  Brown D, Holtbecker R, 2007. New ferry

concepts reduce costs and emissions. Wartsila¨ Tech  

Canova A, Chicco G, Genon G, Mancarella P, 2008. Emission characterization and evaluation of natural gas fuelled cogeneration microturbines and internal combustion engines