Feature 1 | GREEN SHIPPING


is imperative that these pressures and temperatures can be accurately predicted since the chemical formation models, which will follow, are wholly dependent on them. To give an example of the success the approach to date, Figure 6,


of


compares the predicted power card and actual power card for a cylinder of a four-stroke marine diesel engine, running at 600.5rpm, developing 369kW per cylinder. This demonstrates good agreement between the actual and simulated power cards. Once further validation studies, now being conducted, are complete, the emission predictions models, also under development, will be included.


Direct measurements of emissions Another approach to assessing exhaust gas emission levels is to directly measure their production onboard ship. As noted in the base-line methods, there are only limited published data sets of such activities and, since regulations to mitigate ship emissions do not actually require this activity, there has been little imperative to undertake monitoring campaigns more widely.


Clearly there are a number of


barriers to monitoring emissions in real-time on board ship, including the investment required in the equipment and data handling infrastructure, particularly from the perspective of associating the measured emissions values wi th


the other causal


parameters which would be required for meaningful interpretation of the data. Additionally, caution should also be exercised in interpreting the results since the equipment for monitoring and measuring exhaust gas emissions can often return results with high levels of variability. Besides the te chnical and


financial challenges of using direct measurements for assessing emissions factors and indices, there may be reluctance to voluntarily undertake this activity from a commercial perspective. In particular there is a risk of negative perceptions if high emission levels are revealed under realistic operational conditions, as opposed to maintaining a conservative


stance of correctly


meeting (or nominally exceeding) regulatory requirements, which require no subsequent reporting of actual emissions produced.


Emissions indices To date, the principal mechanism for controlling (with the intension of reducing) exhaust gas emissions from ships is through the IMO MARPOL ANNEX VI and, where relevant, regional regulations. These regulations have set nominal rated limits on engine design (for NOx) and fuel quality limits (for SOx), but do not require measurements or monitoring of


the


actual emissions produced in operation and therefore, under this regime, as Figure 7 demonstrates, operational choices will ultimately dictate the actual levels of these emissions from


Figure 6: Comparison between a power card taken from cylinder of a four-stroke marine diesel engine, A, and the simulated power card for the same specification, overlaid on the original power card, for comparison, B.


44


ships. In addition, more recently, the concept of efficiency indices (EEOI and EEDI) has emerged to encourage a reduction in GHG (CO2


) emissions


from ships through reducing fuel usage per unit transport effort. Although, since minimising fuel usage is already financially in the best interests of the shipping companies, one could suppose that there is limited scope for further reduction through this strategy alone and as has been shown in other studies, again, as noted in Figure 7, might actually be in conflict with other emission reductions. While many technologies exist at


differing technology readiness levels to reduce exhaust gas emissions from ships, as the issues and regulations for exhaust gas emissions control from shipping increases it will become ever more important to establish the tools, methods and strategies for predicting, measuring and controlling exhaust gas emissions. Tis paper has highlighted the various


alternatives and shown that the level of sophistication for applying such methods can be appropriately chosen to fit a broad spectrum of desired outcomes – from relatively simple and aggregated base-line methods, to potentially, highly sophisticated prediction methods that could be used to optimise the detail of operation or design of individual ships – which if adopted or more widely available, will no doubt have the consequence of making a net reduction in harmful emissions – particularly in regions where the emissions cause most harm. NA


This work was conducted within the Clean North Sea Shipping Project (CNSS), www.CNSS.no. The authors wish to thank and acknowledge the support for this work from the European Commission, Regional Development Fund, Interreg IVB North Sea Region Programme, 2007-2013. The authors wish to thank and


acknowledge the support for this work from the European Commission, Regional Development Fund, Interreg IVB North Sea Region Programme, 2007-2013.


The Naval Architect May 2012


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