Unmanned Systems Technology 002 | Scion SA-400 | Commercial UAV Show report | Vision sensors | Danielson Trident I Security and safety systems | MIRA MACE | Additive manufacturing | Marine UUVs

52 complications such as variable geometry – and are sized to meet the needs of the dual boosting process; no wastegate is required. The three-into-one exhaust manifold feeding turbo two is a stainless steel production made in-house. With the two-stage compression, plenum pressure is as high as 4.0 bar absolute and the compression ratio is 15:1. That ratio might not be high by CI standards but it has to be seen in the context of the plenum pressure, implying an extremely high effective compression ratio. As is normal in this type of engine, the combustion chamber is bowl-in- crown, with in this case the geometry optimised for maximum fuel mileage. The only concern regarding emissions is that there should be a lack of visible smoke. The two valves serving each cylinder are upright, so it follows that the piston crown can be flat aside from the central bowl, which in any CI engine forms much of the combustion chamber at TDC. The injector is arranged to fire directly into the bowl. The geometry of the porting is crucial from the point of view of creating the appropriate turbulence in the charge air as it enters the cylinder, while the geometry of the bowl is crucial to combustion effectiveness. Since this is a CI engine, the only throttling of the charge air is a butterfly for emergency cut-off only; engine load is governed purely through adjustment of the fuelling. In this day and age, one would expect the Trident engines to be electronically controlled, as indeed are all advanced automotive engines produced by Danielson, whether CI or SI. An engine management system is particularly significant in the context of an SI engine, allowing coordinated control of the injection, the ignition and often these days a fly-by-wire throttle. While the CI engine avoids the need for spark plugs and a throttle, computer-based control of its injectors is clearly theoretically advantageous. On the other hand, in the UAV environment there is a huge danger of interference between electronic engine control and the other electronics operating the craft and its sensors. “A UAV is full of electronics,” Hubschwerlen points out. “If you have mechanical engine control you will have no compatibility problems, and with fewer components in the engine package you will have inherently better reliability. The lack of electronics makes the injection system immune to electromagnetic interference.” Hubschwerlen adds that, in the event of any system problem, using a common rail served by a single pump would put the engine entirely out of action. That danger is avoided by each cylinder having its own independent injection Spring 2015 | Unmanned Systems Technology The Trident TD2 nestling in a typical UAV airframe