Emulsion trial could spark new interest

A chief engineer records in-cylinder pressures while under load running on fuel oil emulsion. A chief engineer records in-cylinder pressures while under load running on fuel oil emulsion.

The idea of using emulsified fuel has been around for decades, and a recent trial has again demonstrated that efficiency gains are possible alongside the known emission reductions, writes Wendy Laursen

An Australasian ferry operator has recently trialled the use of emulsified fuel and hired an independent scientist to verify the results. The conclusion: fuel savings of 5% at high loads and significant reductions in NOx and particulate emissions, says Leigh Ramsey, director of Blended Fuel Solutions New Zealand. The results are in keeping with research that goes back decades, where a range of universities and companies have reported reductions in fuel consumption of 1% to 8%.

Mr Ramsey is the Australasian distributor for the emulsion system developed by Alternative Petroleum Technology (APT) of the US. The system provides for greater atomisation of the fuel through the vaporisation of water. This is said to give a cooler and more complete combustion. 

Unlike base fuels, when emulsified fuel droplets are sprayed into the combustion chamber, they are atomised a second time as a result of the violent transformation of their water content into steam. This shatters the petroleum surrounding that water into much smaller droplets. Smaller droplets have a much greater surface area, significantly improving the efficiency of combustion. 

A secondary effect of water transforming into steam is that peak combustion temperatures are reduced, resulting in the formation of significantly less NOx gas. The changes in combustion kinetics also significantly reduce particulate matter emissions that result from incomplete combustion. 

Depending on the engine type, age and condition, service history, maintenance, duty cycles and on the water content of the emulsion, testing has demonstrated 10% to 30% NOx reductions, 10% to 60% CO reductions, 60% particulate reductions and 2% to 8% CO2 reductions. Visible smoke is also virtually eliminated. 

APT’s emulsified fuels are a blend of traditional liquid fuels such as diesel, naphtha, heavy fuel oil or biodiesel, and water. In diesel or biodiesel-based emulsions, sub-micron water particles are entrained in the petroleum through a high-shear blending process that employs a surfactant additive to bond the water and petroleum together in a stable emulsion. Depending on its application, the water content of APT’s emulsions can vary between 2% and 20% by volume. However, the standard product for diesel engines contains about 10% water and less than 1% additive for fuel oil applications.

The emulsifier uses a combination of shear and cavitation forces to achieve a finely and thoroughly dispersed suspension of water in the oil. The size of water particles in the emulsion is critical, with the best results gained by 2 to 4 picometre diameter droplets. 

APT blending units can be sized up or down to meet the needs of its customers. However, common APT blending units for the production of emulsified fuels produce between 180 and 30,000 litre/h and can be tailored to suit individual users needs.

The APT blending unit computer measures, monitors and controls a variety of operating parameters including temperatures, pressures, flow rates and motor variables. If any of the parameters vary from pre-set operational limits, an alarm will notify the operator. If a change is not made within a set period the unit will automatically cease production. To ensure consistent product quality, the operator has only limited access to operational parameters.

Blending units are relatively inexpensive, simple to manufacture and operate with minimal service and maintenance requirements, says Mr Ramsey. Once installed, it is not necessary to operate the desk-sized system continuously. It can easily be switched on and off to suit operating profiles such as entry into or exit from ports if needed.

“Shipboard operation is very easy. You’ve got large tanks and you can blend on board to a day tank,” says Mr Ramsey. No engine modifications are required. However, as there is a slight delay in ignition, the engine tuning could be adjusted slightly if desired. The system is suited to both two- and four-stroke engines. “The lower the speed of the engine, the longer the fuel sits in the cylinder and the better the results,” he says.

Emulsions generally give little advantage to boiler efficiency if good atomisation is already established or if distillates or diesel fuels are used, but they can help to maintain uniform efficiency over time and can improve fuel economy if residual fuel is burnt. They can also be beneficial at low load because most burners fail to atomise properly under these conditions. 

The quality of water required for emulsifying the fuel used in boilers is not critical. Potable, condensate or reasonable waste water can be used, but water quality for diesel engines should be potable with less than 5% dissolved solids. Water temperature requirements are not critical 
 
Past tests on a container ship owned by United States Lines demonstrated that the requirements for making water on board did not place extra burden on the ship’s evaporators. A University of Newcastle study predicted that distilled water could be provided from a flash evaporation unit operated on waste heat from the engine jacket water coolant of slow-speed diesels.

Emulsions don’t lead to SOx emission reductions specifically but, APT is working on that. The company has developed a process called Oxidative Desulfurization (ODS) which it claims is cheaper than existing refinery techniques. Little heat and pressure is required. Rather, hydrogen peroxide is used as a catalyst to oxidise sulphur which can then be removed using a solvent. The system has been tested for a range of distillate fuels and fuel oils, and APT and Blended Fuel Solutions New Zealand are seeking partners to commission a pilot plant.

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