INTRODUCTION
Since the creation of the internal combustion engine, engineers began to explore different paths to increase the engine power output and overall thermal efficiency. One of those paths was by precompressing the combustion air through a device which nowadays is well known in the engineering world, the turbocharger.
The turbocharger is a turbine-driven forced induction device that pushes extra air into the combustion chamber to improve the engine performance. Alfred Buchi, a Swiss engineer, was the first to successfully implement a turbocharger, achieving a power increase of more than 40%.
The turbochargers were first used in very large engines such as marine ones. As time went by, they started to be more popular due to their big advantages on performance and fuel consumption and emissions reduction over naturally aspirated engines. On top of that, in the 70’s Formula 1 cars started using turbochargers, therefore, their reputation increased considerably among the automobile and motorsport industries.
The engineers of today are looking at some other ways to improve the internal combustion engine efficiency by addressing the weak points of conventional turbochargers such as “turbo lag”. As a result, two new devices have been presented to the market in the past years (2017), the eBooster and the eTurbo.
This blog post carries out a comparison between the eBooster and the eTurbo, equally, a second comparison is done to highlight their attributes over a conventional turbocharger. To analyse this, DYMOLA and some related MODELICA libraries such as VeSyMA – Engines are used as the main tools for the investigation.
EBOOSTER
It can be defined as a device which assists the conventional turbocharging systems by improving the boost pressure and the transient engine response, particularly at low rpms. Unlike the eTurbo, this is not coupled to the turbocharger turbine and is therefore allowed to operate independently.
Operation
- When the vehicle is running at low load and constant speed, the eBooster is inactive. The Bypass valve is closed.
- As soon as the driver presses the accelerator pedal, the eBooster enters in action providing near instantaneous boost pressure. The Bypass valve is open, therefore the already compressed air goes through a second compression stage when it gets to the eBooster.
- Once the turbocharger matches the eBooster boost pressure, the eBooster is switched off. The Bypass Valve is closed.
It must be stated that the turbocharger is under normal operation throughout all the previous three phases. Likewise, the bypass valve is the one in charge of directing where the compressed air flow goes.
ETURBO
It consists of an ultra-high-speed electric motor that works in conjunction with a conventional turbo. This device assists the turbocharger at low rpms in order to dramatically reduce the turbo lag by spinning the compressor and therefore, injecting a considerable amount of airflow into the system. Likewise, it recovers wasted energy from the turbine.
PROS & CONS
The only difference between the two devices relies on the eTurbo capability of recovering energy wasted by the turbine spin.
EBOOSTER IN DYMOLA
A Turbocharged 4-cylinder 1800cc engine template was taken as a starting point for the model in DYMOLA. An eBooster and a bypass valve were fitted between the compressor exit and the intercooler entrance. A new control strategy was set up for their operation which works based on the throttle opening and pressure ratio across the eBooster.
ETURBO IN DYMOLA
A Turbocharged 4-cylinder 1800cc engine template was taken as a base in DYMOLA. An electric motor was coupled to the turbocharger shaft and a new control strategy was created for it within the turbo controller based on the throttle opening and plenum pressure.
RESULTS
Three different simulations were run using the same type of engine coupled to different air forced induction devices. The experiment conditions were identical in every case.
The experiment consists of an engine coupled to a simple chassis dyno. The engine is accelerated with wide-open throttle for 3.5 seconds from t=0.5 seconds. The vehicle initial speed was set to 5 km/h and the maximum boost pressure was limited to a maximum of 2.3 bars. The maximum boost limit is a function of engine speed and load.
The results collected are the following (Fig. 6). The charts show the next scenario.
Case 1 – Plots in green – conventional turbocharger
Case 2 – Plots in red – eBooster
Case 3 – Plots in blue – eTurbo
The charts display vehicle speed [km/h], plenum pressure [Pa] and engine speed [rpm] correspondingly.
ANALYSIS
The results show a clear gain in speed for the eBooster and eTurbo models after the second 0.8 compared to the conventional turbo, with a peak difference of around 15 km/h. The eBooster model reaches the highest top speed. For the plenum pressure, the eBooster and eTurbo once again show their superiority. Both models register a considerable difference in pressure compared to the conventional turbo with a peak difference of around 100,000 Pa at around t=1.4s, a fact that helps to reduce the turbo lag. The eBooster reaches a higher plenum pressure than the eTurbo, however, the eTurbo shows a more steady line (second 0.6 to 1.2). Finally, the engine speed chart shows how due to the increase in torque at low rpms the eBooster and eTurbo models are able to change gear earlier compared to the conv. turbo. The first two models change gear at around t=1.85s meanwhile the conv. turbo change until around t=2.35.
CONCLUSIONS
The eBooster and eTurbo clearly address the weak points of conventional turbochargers as both devices are capable of reducing the turbo lag and provide an increase in torque at low rpms, hence, improving the overall drivability.
In terms of which of the two inventions is better, it all comes down to the intended application. On one hand, the eBooster operation strategy is less complex than the eTurbo but it does not offer the recovering energy capability. On the other hand, the eTurbo offers higher performance than the eBooster but it adds a more complex electrical system operation.
Another topic to point out is reliability. These components are relatively new, this means they require an extensive testing and calibration plan in order to meet the agreed performance and the industry safety standards.
CURRENT APPLICATIONS
Formula 1 – eTurbo
Formula 1 is the pinnacle of motorsport and as such it leads the way for future technologies to be tested. Since 2014 eTurbo has been one of them. The introduction of this device under the acronym MGU-H, helped minimise the turbo lag and maximise performance by assisting the compressor with the intervention of a battery.
Audi – eBooster
Car manufacturers such as Audi have already started the implementation of the eBooster or electric supercharger along its model range due to all the advantages previously mentioned.
REFERENCES
- Systems, B., n.d. History | Borgwarner Turbo Systems. [online] Turbos.borgwarner.com. Available at: <http://www.turbos.borgwarner.com/products/turbochargerHistory.aspx>.
- Motorsport Technology. 2018. How Are F1 Engines So Powerful? – Motorsport Technology. [online] Available at: <https://motorsport.tech/formula-1/f1-engines-explained>.
- En.hondaracingf1.com. n.d. Honda Formula 1 Technology | Honda ST13 Power Unit | Honda. [online] Available at: <https://en.hondaracingf1.com/technology.html>.
- f1-Facts, 2020. Renault RS01. [image] Available at: <http://f1-facts.com/gallery/p/JJabouille>.
- Borgwarner. (2017). eBooster. [Image] Available at: https://www.borgwarner.com/technologies/electric-boosting-technologies.
- Borgwarner. (2017). eTurbo. [Image] Available at: https://www.borgwarner.com/technologies/electric-boosting-technologies.
- f1-Facts, 2020. Renault RS01. [image] Available at: <http://f1-facts.com/gallery/p/JJabouille>.
- WRC Motorsport & Beyond, 2020. Audi RS6. [image] Available at: <https://wrc.net.pl/mz-youtuber-uwolnil-z-kaganca-600-konne-audi-rs6-c8-i-sprawdzil-ile-faktycznie-pojedzie-na-niemieckiej-autostradzie>.
Written by: Jose Miguel Ortiz Sanchez, Project Engineer
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