Phase Two Testing

Phase two of testing intended to investigate the performance of the engine modifications, as well as test the performance of the Chinese style engine. The primary modification tested was the expanding tail pipe for the adjustable FWE engine, which was tested at various engine lengths to determine best engine performance. The ceramic coating on the fixed length FWE engine was also tested to determine any changes in performance.

Effectiveness of an expanding tail pipe on an FWE engine

After the results of the first round of testing, the adjustable FWE engine configuration failed to produce 2kg of thrust. In order to improve the thrust of this engine an investigation into the effect of an expanding exhaust section was conducted. Tests were conducted to compare the performance of the test engine from 2007, to the

equivalent engine, with an expanding exhaust section. Short lengths of 50mm diameter pipe were cut to allow for fine tuning of the exhaust section.

Figure 116 - The adjustable FWE engine with expanding tail section and 100mm extension.

Initially the expansion section was added to the original FWE engine, with an additional 100mm extension section added to the exhaust, as shown in Figure 116. The engine length was then increased in 50mm and 100mm intervals, to determine the most suitable operating conditions. Based on the results, the most effective length was then selected, and 25mm sections were added and removed in order to find the optimal length of the engine. The results are summarised in Table 19.

Table 19 - Expanding Exhaust Test Results

Section Length

(mm) 100 150 300 325 350 375 400 450 650

Max Thrust (kg) 1 3 3.25 3.3 3.55 3 3 3.2 2

From the tests it was concluded that a total exhaust length of 1080mm was optimum for this configuration, producing 3.55kg of thrust, achieving both the project goal of producing an engine with 3kg of thrust and extension goal of achieving 3.5kg of thrust.

The results suggest that the engine is also less sensitive to changes in exhaust length, which is beneficial from an engine design point of view.

Testing of the expansion section also revealed that the engines were extremely throttle able, with numerous engine configurations still maintaining self sustained combustion to as low as 0.5kg of thrust. This is a significant achievement, as a throttle able engine will give an aircraft more control during flight.

Section 6.1 Engine Testing

The effect of the intake length was planned as an additional investigation, however during the final testings, a failure of the main fuel cut-off valve occurred, which jeopardised the safety of the remaining tests, hence the tests were aborted.

Test Chinese Engine for thrust measurement

The Chinese engine, which was manufactured after the mixed success of the first round of testing, was tested to determine the engines maximum thrust, most effective injector position, and throttle range.

Ten tests were performed on the Chinese engine, with the main aim of determining a suitable injector position for producing maximum thrust. The fuel consumption and throttle range of the engine were also of interest.

Seven different injector positions were tested, with the results shown in Figure 117. It was noticed during testing that as the injector position was moved into the engine, the engine became more throttle able, with the engine throttling as low as 0.8kg on several occasions. The engine was also easier to ‘flame out’, which suggested the fuel consumption of the engine was less, however data could not be collected regarding this due to issues encountered with the load cell.

Thrust vs Injector Position

Figure 117 - Affect of injector position on engine thrust

Maximum thrust was achieved with the injector positioned at 32mm inside the engine intake, with a maximum thrust of 3.62kg achieved. The results from this test can be seen in Figure 118.

Figure 118 - Thrust Results

A fuel consumption test was performed at this intake position, yielding a specific fuel consumption of 5kg/kg/hr. It is expected that better results can be achieved by moving the injector position further into the intake.

Effect of Ceramic coating on Engine Performance

In an attempt to reduce the temperature of the engine, the interior of the larger FWE engine was ceramic coated by Ceramic Coats Australia. The ceramic coating was intended to reduce heat transfer to the metal, in an attempt to reduce the need for heat shielding on the aircraft.

Four tests were performed on the ceramic coated engine, with thrust results of 1.3kg achieved, which was similar to the results from the first stage of testing. From video footage it could be determined that the engine ran visibly cooler, however it was noticed that damage occurred to the ceramic coating after several runs (Figure 119). It is anticipated that the ceramic coating applied was not suitable for the temperatures

Section 6.1 Engine Testing

achieved in the pulsejet. Further investigation is required to determine if ceramic coating is a feasible option for reducing the temperatures experienced by the engine structure.

Figure 119 - Visible damage to ceramic coating

Conclusion

The second phase of testing was successful, with two engines achieving the projects extended goal of 3.5kg of thrust. Specific fuel consumption figures of 5kg/kg/hr were also promising, as they showed improvement on both results from the studies of Coombs et al, who recorded 7.1kg/kg/hr at 1.6kg of thrust, and Enics pulsejets, which advertise figures of 6.6kg/kg/hr for their engines.

The testing program proved that an expanding exhaust is capable of improving the performance of an engine; however significant work must still be conducted to determine a method for optimizing the length and expansion of these sections.

Finally the tests showed that ceramic coating is an option for reducing the heat transfer out of the engine, with similar thrust results achieved for the engine with and without ceramic coating. However the damage to the coating suggests that more research into the most suitable coating for the engine must also be conducted before this is added to the flight weight engine. The added weight of the engine must also be determined.

A full report of all tests can be found in Appendix H – Test Log Books