Reduction of Emissions From a High Speed Passenger Ferry

Emissions from marine vessels are being scrutinized as a major contributor to the total particulate matter (TPM), oxides of sulfur (SOx), and oxides of nitrogen (NOx) environmental loading. Fuel sulfur control is the key to SOx reduction but NOx and PM production are primarily engine design dependent. Significant reductions in the emissions from on-road vehicles have been achieved in the last decade and emissions from these vehicles will be reduced by another order of magnitude in the next five years. These improvements have served to emphasize the need to reduce emissions from other mobile sources, including off-road equipment, locomotives, and marine vessels. Diesel-powered vessels of interest include ocean-going vessels with low- and medium-speed engines, as well as smaller vessels with medium- and high-speed engines. A recent study examined to use of intake water injection (WIS) and ultra low sulfur diesel (ULSD) fuel to reduce the emissions from a high-speed passenger ferry in southern California. One of the four Detroit Diesel 12V92 two-stroke, high-speed engines that power the ferry was instrumented to collect intake airflow rate, fuel flow rate, shaft torque, and shaft speed. Engine speed and shaft torque were uniquely linked for given vessel draft and prevailing wind and sea conditions. A raw exhaust gas sampling system was utilized to measure the concentration of NOx, carbon dioxide (CO₂), and oxygen (O₂), with a mini dilution tunnel sampling a slipstream from the raw exhaust was used to collect TPM on 70 mm filters. The emissions data were processed to yield brake-specific mass results. The emissions measurement system that was employed allowed for redundant data to be collected for quality assurance and quality control. To acquire the data, the ferry was operated at five different steady-state speeds. Three modes were executed in the open sea off Oceanside, CA, idle and harbor modes were also selected for the test matrix. Data have showed that the use of ULSD along with water injection (WIS) could significantly reduce the emissions of NOx and PM while not affecting fuel consumption or engine performance, when compared to baseline marine diesel fuel. The results showed that a normal 40% reduction in TPM was realized when switching from marine diesel fuel to ULSD. A small reduction in NOx was also shown between the marine fuel and the ULSD. The implementation of the WIS reduced NOx by 11% to 17%, depending upon the operating condition. With the WIS, TPM was reduced by a few percentage points, which was close to the confidence level of the measurements.