GEN 002 Testing & Evaluation

  The objectives of the Phase 1 testing program were:

• Evaluate the compression performance of the engine
• Implement high pressure common rail fuel injection system controlled by prototype engine control module
• Demonstrate compression ignition of diesel fuel

Compression Testing

For this phase of the testing, the engine was motored by the dynamometer at speeds up to 500 rpm to evaluate the compression performance of the engine and to evaluate the effectiveness of the seal systems. The engine was instrumented with Kistler pressure transducers located in the leading and trailing volumes as illustrated below. As the engine was motored, pressure data was recorded at a sampling rate of 10 kHz; therefore, a thirty-second test produced 300,000 data points.

A snapshot of data taken during one of the compression tests is shown below. The data shows that the engine is compressing the air, although the maximum pressure is less than analysis predicts. This indicates that the side seal system is allowing leakage which leads to reduced compression pressures. The near vertical increase in pressure in the leading volume indicates that the Roton tip seals are performing as intended as the Roton comes into contact with the housing surface on the leading volume side of the apex of the housing. This figure also indicates a variation in the effectiveness of the Roton tip seals from one Roton to the next, illustrating that improvement in their performance is possible with improved fit, resilience, etc.

Demonstration of Compression Ignition

For this phase of the testing, the engine was motored by the dynamometer at 600 rpm, which is a typical idle speed for diesel engine. In order to minimize the number of variables that would influence these initial tests, only one chamber of the engine was fueled. Fuel was injected at 6000 psi, with the start of injection at 12° before top dead center and a duration of 1.5 milliseconds, which corresponds to an approximate 40:1 air/fuel ratio. This lean operating condition was chosen to minimize the combustion pressure during these initial tests. To eliminate the effects of scavenging, the engine was force-aspirated at atmospheric pressure.

Click Here To View The Legacy Engine Being Tested (2.18Mb Download)
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The figure below shows one complete thermodynamic cycle. The maximum pressure achieved exceeds 700 psi; this pressure should be evaluated with respect to the air/fuel ratio. The pressure trace indicates the evaporative cooling of the air due to the injection of the fuel, continued compression and ignition. The pressure at the start of combustion is approximately equal to the maximum pressure achieved during the compression testing, which indicates that the injection timing is adequate for this engine speed and air/fuel ratio. Further optimization of the injection timing will be conducted in the next phase of the test program, along with multiple injections. The prototype engine control module is capable of up to five injection events per cycle.

 

  The figure below shows six complete thermodynamic cycles. The same features related to injection are evident in this pressure plot. Combustion pressures for this series of cycles vary, which is an indication of the variability of the seal performance from Roton to Roton. Determining the root cause of this variability was one objective of the Phase 1 post-test disassembly of the engine. The results of the examination of the engine are detailed below.

 

Post-testing Evaluation

At the conclusion of the planned Phase 1 tests, the engine was disassembled and examined. There were two major issues identified which directly correlate to the lower than expected compression pressures and the variability from Roton to Roton.

Leakage paths were identified in the side seal system which allow air to escape into the preceding volume. Damage to the Roton tips seals was discovered which was attributed to a loss of Roton-to-rotor alignment during the tests. Modifications to the engine to correct these issues have been designed and are in the fabrication process. Phase 2 testing will commence as soon as the engine is modified and reassembled.

Conclusion

The three objectives of the Phase 1 test program have been achieved. The compression performance of the engine has been evaluated and steps are underway to improve the performance of the seal systems. The fuel injection system and prototype engine controller have been successfully demonstrated. Compression ignition of diesel fuel has been successfully demonstrated during multiple Phase 1 combustion tests.