Determination of Emissions from a Very Large Crude Carrier Using Two Different Fuels

Background OGVs are significant contributors to California statewide emissions of diesel particulate matter (PM), diesel PM with aerodynamic diameters less than 2.5 micrometers (PM2.5), nitrogen oxides (NOx), and sulfur oxides (SOx). In response to growing concerns regarding the emissions of OGVs, California enacted a regulation in 2008 to require the use of lower sulfur marine distillate fuels. This regulation, the OGV Clean Fuel Regulation,1 requires vessel operators within 24 nautical miles (nm) of the California coastline and islands to use cleaner low sulfur distillate fuels (either marine diesel oil or marine gas oil) in their main engine, auxiliary engines, and auxiliary boilers. The fuel standards are implemented in two phases. Beginning January 1, 2014, the fuel sulfur limit was ≤ 0.1% sulfur by weight. On March 26, 2010, the International Maritime Organization (IMO) officially designated waters of the United States and Canadian coastlines as an Emission Control Area (ECA) pursuant to Annex VI of the MARPOL Convention. Within the ECA boundary which extends 200 nm offshore, vessels are required to use lower sulfur fuels. Unlike the California OGV Clean Fuel Regulation, the ECA does not specify what type of fuel; rather it establishes a limit only on the fuel sulfur level. The ECA began implementation in August 2012, with a 1 percent sulfur limit that then dropped to a ≤ 0.1% sulfur limit on January 1, 2015. While it was expected that most vessel operators would use low sulfur marine distillate fuels such as MGO or marine diesel oil (MDO) to comply with the ECA, a new low sulfur heavy fuel oil (HFO) has been marketed and made commercially available that can meet the ECA fuel sulfur requirements. The California Air Resources Board is interested in assessing the emissions impacts of switching to this new low sulfur HFO. Approach The overall objective for this evaluation was to determine and compare emissions from fourstroke diesel electric marine engines operating on a ≤ 0.1% sulfur by weight HFO and a ≤ 0.1% sulfur by weight MGO. The study required a vessel for the test platform and a shipping company provided a vessel representative of the very large crude carriers (VLCC) that operate throughout the world. Testing took place as the VLCC travelled from the Port of Los Angeles to Port Angeles, WA. Sampling of the actual in-use emissions of gases (CO2, CO, and NOx) and particulate matter (PM2.5) mass from each of two main generator engines was in compliance with the ISO 8178-2 protocol while the engine operating conditions followed the ISO 8178-4 D2 certification test cycle. Results Overall nitrogen oxide (NOx) emission factors were 10.2±0.08 g/kWh and 10.7±0.03 g/kWh for HFO and MGO respectively, which are both well below the Tier 1 NOx standard of 12.9 g/kWh for a medium speed, 512 rpm engine. Additionally, the NOx emission factors measured in this study are well below the 18.7 g/kWh and 18.1 g/kWh emission factors specified by Lloyds services data and the US EPA/ARB for main engine OGVs.

1 Fuel Sulfur and Other Operational Requirements for Ocean-Going Vessels within California Waters and 24 Nautical Miles of the California Baseline. title13, California Code of Regulations (CCR) §2299.2 and title 17, CCR §93118.2.

The PM2.5 emission factors were 0.62±0.01 g/kWh for HFO and 0.20±0.02 g/kWh for MGO which are well below those listed by Lloyds service data (1.23 g/kWh), US EPA (1.08 g/kWh) and CARB (1.5 g/kWh) due to the very low sulfur content of HFO used in this study. PM was composed mainly of organic carbon (OC) for both fuels with very little elemental carbon (EC) present. BC emissions were not statistically different between the HFO and MGO where both fuels showed the highest EF at 10% load (~ 0.15 g/kWhr) and lowest at higher load points (~ 0.01 g/kWhr). Real-time soot measurements with the AVL micro-soot sensor (MSS) and EC analyzed by NIOSH method agreed very well with R2 values of 0.99 while real-time PM with the PPS-M sensor were 40% and 57% lower than gravimetric PM2.5 for HFO and MGO.

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