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Orbital Engine Company
Report to Environment Australia, February 2003
This document presents findings of testing a sample of ten Mercury Marine 15hp two-stroke outboard marine engines with gasoline containing 10% and 20% by volume ethanol (E10 and E20), completed by Orbital Engine Company. The program is an initiative of the Environment Australia project 'Market Barriers to the Uptake of Biofuels - Testing Petrol Containing 20% Ethanol (E20).' The program of work as reported here, was initiated from findings of a previous program of work reported upon and submitted to Environment Australia, 'A Testing Based Assessment to Determine the Impacts of a 10% and 20% Ethanol Gasoline Fuel Blend on Non-Automotive Engines' (1) completed by Orbital Engine Company. This previous program identified that the Mercury engine would stall during an on-water driveability assessment when operated on the E20 fuel blend. The stall occurred upon demand of Wide Open Throttle (WOT) acceleration after a test designed to assess the engines performance during in-gear low speed motoring. The motoring test duration is at least 10 minutes and is conducted at two different engine speeds.
Based on the sample of ten engines, the work reported here presents the statistical significance of the stall behaviour in terms of the likely impact on the general population of this engine type. The sample size also presented the opportunity to report on other on-water driveability defects related to E20 and E10 fuel blends.
In general, engine testing with the E10 fuel blend has detected little performance difference when compared with operating the engines with ULP gasoline only. The only area where a substantial impact has been identified was during demand of WOT acceleration following the in-gear low engine speed motoring test at the lowest of the two engine speeds tested. One out of the ten engines tested stalled. The statistical inference of this is to a 95% confidence level; between 0.53 and 38.1% of the general engine population of this particular engine type will experience stalling upon demanding WOT acceleration following the in-gear motoring test.
For the E20 fuel blend, the stalling characteristic was found to occur at both the engine speeds tested. For the WOT acceleration demand following lowest test speed, three of the ten engines tested stalled. The statistical inference to a 95% confidence level is that between 9.4 and 58.7% of the general engine population of this particular engine type will experience stalling. At the higher test speed one out of the ten engines tested stalled, the statistical inference to a 95% confidence level is that between 0.53 and 38.1% of the general engine population of this particular engine type will experience stalling. This engine stall characteristic presents the potential to impact on reliable engine operation. It must however be noted that all engines that stalled could be restarted immediately upon operation of the engines starting mechanism allowing acceleration of the boat.
All engines tested for WOT acceleration following the in-gear motoring test at both engine speeds accelerated the boat without hesitation when operating with neat gasoline.
The on-water testing program revealed increasing degraded performance with increasing ethanol content of the fuel blends when compared with the performance utilising gasoline only. While operating the engines on the E20 fuel blend the following operating characteristics were observed: