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In 1990, Roy Douglas developed an analytical method to calculate the global air-to-fuel ratio of a two-stroke engine from exhaust gas emissions. While this method has considerable application to two-stroke engines, it does not permit the calculation of air-to-fuel ratios for oxygenated fuels. This study proposed modifications to the Roy Douglas method such that it can be applied to oxygenated fuels. The ISO #16183 standard, the modified Spindt method, and the Brettschneider method were used to evaluate the modifications to the Roy Douglas method. In addition, a trapped air-to-fuel ratio, appropriate for two-stroke engines, was also modified to incorporate oxygenated fuels. To validate the modified calculation method, tests were performed using a two-stroke carbureted and two-stroke direct injected marine outboard engine over a five-mode marine test cycle running indolene and low level blends of ethanol and iso-butanol fuels.

Biologically derived isobutanol, a four carbon alcohol, has an energy density closer to that of gasoline and has potential to increase biofuel quantities beyond the current ethanol blend wall. When blended at 16 vol% (iB16), it has identical energy and oxygen content of 10 vol% ethanol (E10). Engine dynamometer emissions tests were conducted on two open-loop electronic fuel-injected marine outboard engines of both two-stroke and four-stroke designs using indolene certification fuel (non-oxygenated), iB16 and E10 fuels. Total particulate emissions were quantified using Sohxlet extraction to determine the amount of elemental and organic carbon. Data indicates a reduction in overall total particulate matter relative to indolene certification fuel with similar trends between iB16 and E10. Gaseous and PM emissions suggest that iB16, relative to E10, could be promising for increasing the use of renewable fuels in recreational marine engines and fuel systems.

This study evaluates iso-butanol as a pathway to introduce higher levels of alternative fuels for recreational marine engine applications compared to ethanol. Butanol, a 4-carbon alcohol, has an energy density closer to gasoline than ethanol. Isobutanol at 16 vol% blend level in gasoline (iB16) exhibits energy content as well as oxygen content identical to E10. Tests with these two blends, as well as indolene as a reference fuel, were conducted on a Mercury 90 HP, 4-stroke outboard engine featuring computer controlled sequential multi-port Electronic Fuel Injection (EFI). The test matrix included full load curves as well as the 5-mode steady-state marine engine test cycle. Analysis of the full load tests suggests that equal full load performance is achieved across the engine speed band regardless of fuel at a 15-20°C increase in exhaust gas temperatures for the alcohol blends compared to indolene.

Isobutanol-extended fuel was tested in two recreational marine vessels placed in Annapolis, MD and operated for fifty hours on the Chesapeake Bay and surrounding tributaries. Field emissions testing was conducted using a unique portable marine bag sampling system (MPSS) which collected a weighted five mode composite emissions sample consisting of total hydrocarbons (THC), oxides of nitrogen (NOx) and carbon monoxide (CO) while operating recreational boats on both a non-oxygenated baseline indolene certification fuel and a 16.1% isobutanol-extended gasoline. Engine and boat runability was also observed throughout the six month operational period. In addition, back-to-back sampling yielded excellent repeatability from the portable bag sampling equipment. Based on the results of this preliminary study, isobutanol-extended fuels look to be very promising for marine engine applications.

In pursuit of reducing dependencies on foreign oil coupled with U.S. renewable fuel standards and an overall focus and interest in greenhouse gas emissions, investigations continue on feasibility of replacement biologically derived fuels such as ethanol and butanol. Majority of existing recreational products such as marine outboard engines, boats, personal watercraft, all terrain vehicles and snowmobiles are carbureted or operate open-loop, meaning the engine does not have the capability to sense air-fuel ratio. Ethanol has a specific energy content that is less than gasoline. Without means to compensate for air-fuel ratio requirements of specific fuels, open-loop engines may suffer from a condition known as enleanment, in which catastrophic engine failure may result. On the contrary, butanol has specific energy content closer to that of gasoline, suggesting open-loop engines may be less prone to negative effects of increased biologically derived fuel concentrations in gasoline.

Recently, outboard engine technology has advanced significantly. With these new technologies comes a substantial improvement in emissions compared to traditional carbureted two-stroke engines. Some two-stroke gasoline direct injection (GDI) marine outboard engines are now capable of meeting California Air Resources Board 2008 Ultra-Low emissions standards. With improvement of gaseous emissions, studies are now being conducted to assess particulate matter (PM) emissions from all new technology marine outboard engines which include both four-stroke and two-stroke designs. Methods are currently being developed to determine the best way to measure PM from outboard engines. This study assesses gaseous and PM emissions, mutagenic activity of PM and oil consumption of two different technologies over the useful life of the engines.

Carbon Monoxide (CO) has become a pressing issue for the recreational marine industry. An increasing number of boating incidents have been linked to CO poisoning caused by emissions from gasoline-powered marine engines. Measurements by the National Institute for Occupational Safety and Health (NIOSH) and the U.S. Coast Guard have confirmed potentially hazardous CO concentrations near many of these engines. The measurements have also shown much lower CO concentrations for Evinrude® two-stroke direct-injected engines. This paper reviews national and international CO emission regulations for marine engines and discusses CO formation and reduction mechanisms. The differences between homogeneous- and stratified-charge combustion systems on CO formation, resulting from design and calibration criteria, are analyzed.

A method to sample PM emissions from marine outboard engines is a field of ongoing research. This paper details the construction, set-up and operation of a Partial Flow Sampling System (PFSS) to measure total PM emissions from an outboard engine. The PFSS is portable and can be easily moved from one test area to another. It is also cost effective. The results are very promising with less than 2% COV between replicate tests.