Design and Manufacture of an SLS Printed Intake using ETC for FSAE - Samuel Wilson, 2019
Monash Motorsport Final Year Thesis Collection
The Final Year Thesis, is a technical engineering assignment undertaken by students of Monash University. Monash Motorsport team members often choose to conduct this assignment in conjunction with the team.
These theses have been the cornerstone for much of the team’s success. The purpose of the team releasing the Monash Motorsport Final Year Thesis Collection is to share knowledge and foster progress in the Formula Student and Formula-SAE community.
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Summary:
Using a point simulator and analysis of previous results, Monash Motorsport (MMS) has elected to use a KTM 690 Duke R in its 2019 combustion car, M19-C. For the car to achieve a high concept utilisation at competition (ratio of points scoring potential of the car to actual points scored), maximising the power output of the engine and increasing its efficiency is critical. Based on limitations found with the 2018 intake system, the decision was made to utilise SLS 3D printing for intake system production to harness the advantages of virtually unlimited geometrical freedom and reduce manufacturing time and to utilise Electronic Throttle Control (ETC) in preference to a mechanical throttle. This report focuses on maximising the performance of the KTM 690 Duke R, and M19-C, through intake system analysis, simulation and design.
It has been identified that one of the key influences on the volumetric efficiency of an engine is the intake system design, (Norizan et al., 2014) and that the development of a high-performing intake system relies on acquiring and analysing relevant data (Kariotakis, 2011). Previous dynamometer testing and simulation allowed for the selection of geometrical parameters prior to design and removed the need to produce a modular, ‘test intake’ as has been required previously. This previous data and simulation showed that a runner length of 220mm and a plenum volume of 6 litres should be chosen.
Surface-driven CAD, Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD) and Ricardo 1D engine simulation were all used during the design of the intake. This was necessary to utilise the geometrical freedom offered by the SLS 3D printing method. Ricardo confirmed that through the removal of sudden changes in direction and cross-sectional area, the pressure losses through the intake system could be minimised and power and efficiency increased as a result. Surfacing CAD was then used to realise the smooth geometry, and FEA used to guide the structure of the system to minimise mass while meeting stress and deflection targets. Steady-state CFD was attempted on the throttle, restrictor and diffuser but was not largely influential in the design, due to difficulty with meshing and convergence. The design process resulted in a plenum volume of 6 litres and a runner length of 200mm, with the runner length slightly shortened from target for packaging reasons.
The intake system was then installed and calibrated on the Monash in-house dynamometer, where fuel and ignition tables were calibrated, and fuel injector selection undertaken. The Bosch 32mm Electronic Throttle Body (ETB) was also calibrated and data gathered to assist in the creation of the throttle profile. Here, a peak power of 48.6 kW was observed at 8500 RPM and a peak torque of 62.2 Nm at 6000 RPM, representing deltas of 1.5 kW and 2 Nm compared to the 2018 intake system. The system was then installed on M19-C and has performed without fault for over 700km of driving in all weather conditions. Some shortcomings have been realised, and the recommended solutions for these are documented in this report. Data analysis of the system and combustion powertrain as a whole is ongoing to validate and quantify performance compared to M18-C, and physical testing was carried out to validate and calibrate the FEA model. Further refinement of the CFD model was undertaken and recommendations with regards to its use made.
Introduction:
Formula-SAE (F-SAE) is the largest international university design competition in the world. Student teams design, manufacture, test and compete with formula-style vehicles across a range of dynamic and static events, vying for a total of 1000 points (Society of Automotive Engineers, 2019). The static events include cost & manufacturing, business presentation and engineering design, while dynamic events include acceleration, skid pad, autocross and endurance. There are three classes of vehicle permitted in the competition; combustion, electric and driverless, with the former two competing in the events described above and the driverless competing in a modified version of the competition. M17-C and M18-C competed through 2017 and 2018 across a range of events in Australia and Europe and are the most successful Monash Motorsport (MMS) combustion cars to date.
The purpose of an intake system in a combustion engine is to provide clean air to the engine, and, except for direct-injection and diesel engines, facilitate the mixing of the air-fuel mixture prior to entering the combustion chamber. In F-SAE a restrictor is mandated by rules (20mm for 98-RON fuelled vehicles and 19mm for E85) to limit airflow to the engine and therefore limit power output. The restrictor also dictates much of the intake design, as designing a restricted intake carries different challenges and limitations than for a regular, non-restricted intake.
Figure 1: The 2018 F-SAE combustion vehicle from MMS, M18-C (Monash Motorsport, 2018)
The main components of an intake system in F-SAE are; the throttle body, restrictor, diffuser, plenum and runner. The throttle body controls the amount of air flow into the intake system and therefore into the engine, the restrictor restricts the maximum airflow into the system and the diffuser gradually diffuses the air that passes through the restrictor to recover static pressure. The plenum acts as ‘air storage’ which the engine draws from during the intake stroke. Finally, the runner transports air from the plenum to the engine and its length is chosen to take advantage of resonance effects. All these components should be designed to work together to minimise pressure loss through the system and mitigate the effects of the restrictor as much as possible.
M18-C was powered by a 2017 KTM 690 Duke-R single cylinder engine, with a naturally aspirated intake system primarily fabricated from aluminium using a mechanical throttle body. The engine was controlled by a MoTeC M400 ECU that had been in use by the team since 2010. The MoTeC M150, which is an updated ECU with increased functionality over the M400, has been purchased for use in 2019. The M19-C will be using the same powertrain concept as the M18-C and thus the data gained over the last two years can be utilised to direct design decisions of the intake system.
The main limitations identified from M18-C’s intake system stem from its aluminium construction. This includes only being able to achieve simple shapes and geometry, causing sudden changes in cross sectional area which produces pressure losses. The simple geometry also reduces the utilisation of the envelope that the intake is placed in. Inversely, using selective laser sintering (SLS) to produce the intake allows the utilisation of organic shapes and smooth cross-sectional area changes to counteract the limitations stated above. Finally, the use of SLS will greatly reduce manufacturing man-hours compared to fabricating an aluminium intake.
An electronic throttle body (ETB) has been selected in preference to a traditional mechanical throttle body. In conjunction with using the M150, this allows for the implementation of electronic throttle control (ETC). ETC has only become an allowable form of throttle control in F-SAE since 2015 (Society of Automotive Engineers, 2015). ETC offers many advantages over traditional throttle control, primarily in tunability and usability. Launch control can be implemented through throttle position rather than ignition cut, allowing the wheels to stay closer to the target slip ratio and increasing longitudinal acceleration. Custom throttle valve to pedal position maps can be set for different drivers and different events, which is particularly important in an event such as skid pad, where driving at a steady state on the limit of grip is crucial to setting a good time. Idle position can be set into the throttle body, starting can be done by varying throttle position, noise tests can be simplified, and the throttle cable is no longer needed.
Conclusion:
In conclusion, this project has resulted in the successful implementation of a rules compliant ETC system and SLS printed intake system onto M19-C. This has been validated to increase performance compared to the 2018 and 2017 fabricated systems, by increasing peak power by 1.5 kW at 8500 rpm and peak torque by 2 Nm at 6000 rpm.
The use of ETC has greatly improved the ease of starting and idling and has required no work to be done for maintenance at all. This was great improvement over previous years, where hours would be wasted every time the throttle cable needed adjusting. The throttle profile has also been modified from its original setting based on feedback from drivers, who find it more ‘drivable’ than a conventional throttle.
Further refinement of the simulation tools used for design at the beginning of the year has been undertaken and recommendations for further improvements to the tools made to future parts designers. This includes the recommendation to continue using FEA as a primary design tool, but to avoid using CFD apart from as design validation, as the point of diminishing returns can be reached by following good engineering practises for intake design.
One of the largest concerns with moving to a new intake concept for 2019 was reliability. With almost 700 km of racing completed so far, M19-C’s intake system has performed reliably and without issue, confirming the viability of using ETC and an SLS printed system.