World Bunkering >Articles > Fuel management > Adding enzymes: improving quality

Fuel treatment technologies or “chemical additive packages” are the norm and widely used by the petrochemical industry to modify the properties of fuel to enhance performance and stabilise fuels. A wide range of fuel additives with different properties are readily available. A recent series of work on marine diesel engines has demonstrated that microbiology in the form of a complex enzyme formulation in fuel can play a significant part in the conditioning of fuels for improved efficiency and better fuel economy. This work was carried out on two operating ferries, chosen for their modern, state-of-theart diesel engine technology.

Testing

The first set of tests was carried out on a cross-channel ferry Stena Trader, operating between the Hook of Holland and Killingholme in England. The 26,663 gt vessel is powered by two B&W MAN engines with a total power output of 21.6 MW. The ship also has two auxiliary engines running on marine gas oil (MGO) and providing the electrical power. These are Mitsubishi S16R series, V16 engines, each rated at 1,540 kW. The second series of tests were carried out on the 13,256 gt ferry Dokter Wagemaker, operating between Den Helder and Texel Island in Holland, owned by Teso.
She is powered by four 3,600 series 8-cylinder 2460 kW Caterpillar engines. Significantly, the Teso ferry uses an electrical powertrain system, which is instrumented with computerised data logging to record power and fuel consumption and is ideal for this study. During the testing on the Stena Trader, the average fuel consumption and exhaust emissions were recorded on the S16R auxiliary engines on a daily basis over a 65-day period. The MGO fuel was logged from the onboard fuel meters and emissions were measured using a Kane 250 combustion analyser. A baseline was established over the first 14 days, 160 hours, of operation. During this time, untreated MGO was used. The average specific fuel consumption (SFC) was stable at 213 g/kWh and very close to manufacturer’s ratings. Enzyme treated MGO (one part in 10,000) was used starting on day 14 and for the remainder of the test period. Initially, no change was seen in either fuel economy or emissions, with stable results for the next 20 days, 230 hours, of operation.
At this time, there was a notable increase in specific CO emissions, figure 2. This level was maintained for seven days, 80 hours, after which the specific CO emission level dropped by about 50%. At the same time there was a noticeable improvement in SFC to 190 g/kWh, figure 1. This represents a decrease in fuel consumption of 10.8%. This improvement was maintained over the remainder of the test period, 274 hours, with a further improvement to 186 g/kWh. It is clear from these sets of results that there is a very significant improvement in fuel consumption when the enzyme treatment is applied. It is also very interesting that the changes are not seen immediately but that some form of “clean-up” process is involved.

Refining the results

On the Teso ferry, as a baseline, the four identical engines were operated for an extended period on EN590 diesel. Engine performance was checked and found to be very well matched from engine to engine. Subsequently, two engines were switched to running on diesel treated with enzymes (one part in 10,000). Overall fuel consumption was monitored over a nine month period, 3,000 hours of operation. The two engines running on standard diesel consumed about 10% more fuel than those operating on enzyme treated diesel. A more detailed monitoring study was then conducted over a four-month period, 1,600 hours of operation, using biodiesel, B5, treated at 1:10,000. Each engine has a separate fuel tank and so fuel consumption was monitored by recording the fuel during tank filling. Table 1 shows the fuelling records for each engine, along with the hours of operation and the total power output, during this period. Engines #1 and #2 were operating on the treated biodiesel fuel. As can be seen, engines #1 and #2 are showing a much lower SFC than engines #3 and #4 with an average value for engines #1 and #2 of 7.9% less fuel consumed than engines #3 and #4. For the final study on the Teso ferry, it was decided to conduct a detailed monitoring of performance over a typical full day of operation.
The fuel used was biodiesel, B5, and the engines were stabilised for one month (approx. 300 hours) before testing. Two engines were operated on untreated biodiesel fuel and two on enzyme treated fuel (one part in 10,000). During normal operation, the ferry requires the full range of power delivery from the engines from 10% load to full load and hence a full range of fuel consumption. A set of 80 test points were recorded at various points during the test day and SFC results compared from each engine, #2 and #4 during on that day. At full load the values were clustered around 200 g/ kWh, which matches closely with the manufacturers published data. Figure 3 shows a comparison of the difference in SFC between these two engines at the same operating points. The #2 engine running on treated fuel always shows better SFC with an average improvement of 7.4% and a standard deviation of 4.3%. This improved efficiency is further supported by comparing the recorded exhaust gas temperature. The exhaust gas temperature was always lower on the engine burning treated fuel, clearly indicating a better thermal efficiency. The difference in exhaust gas temperature showed an average improvement of 4.7% and a standard deviation of 1.4%.

Improving efficiency; reducing CO²

Based on the test results presented here, it can be concluded that the treating of the fuels with enzyme treatment on board these vessels produced a significant improvement in specific fuel consumption and hence in overall thermal efficiency of these engines, with the associated reduction in CO² emissions. On the Stena Trader, using marine gas oil, an improvement of 10.8% in fuel consumption and hence CO² emissions were seen during a long-term 65-day sea trial and 742 hours of operation. Significantly, this has been maintained after a further approx. 4,000 hours of operation. So this is considered a significant and sustainable reduction in SFC over the original untreated condition. Also, this level of performance shows up to 10.1% lower values than the manufacturer’s published ratings for specific fuel consumption using marine gas oil. On the Teso Texel Island Ferry, an improvement of 7.4% was seen on the comparison between two identical engines operating in tandem and producing very similar levels of power output.
This was further supported by long-term fuel consumption monitoring over a four-month period and an average of 885 hours of operation on each engine. An average improvement of 7.9% was seen between the two engines running with enzyme treated biodiesel fuel and those on untreated biodiesel fuel. The significance in these results was that the enzyme treated biodiesel fuel reinstated the manufacturer’s ratings for specific fuel consumption values, which were originally calculated using marine gas oil.

The authors would like to acknowledge the following who contributed to this article: Marius Overbeeke, Director, Xmile; Dick van der Ent, Energy Saving Engineer, Stena Line BV; Willem Weltevrede, Chief Engineer, Stena Trader, Cees de Waal, Director, Teso.

Specific Fuel Consumption for 65-day period on the Stena Line Trader

Specific CO Emissions for 65-day period on the Stena Line Trader

Improved SFC on Teso Engines