2023 Author: Eric Donovan | [email protected]. Last modified: 2023-05-21 15:44
With its start-stop systems, BMW only recently had the right answer at the right time. On an innovation day, the developers now revealed how fuel consumption should be reduced in the near future.
By Martin Woldt The
fact that modern engines only have an efficiency of just over 30 percent is actually not a glory of modern engineering. After all, it means that more than two thirds of the energy used is lost. But this almost 70 percent, which is burned as waste heat in the engine, cannot be tamed so easily. At its most recent Innovation Day in Munich, BMW presented ideas on how losses can be reduced in the future and internal combustion engines can be made more economical.
Thermoelectric generator
A thermoelectric generator, for example, which is installed in the exhaust system and can generate electricity directly from the exhaust gas heat, is suitable for this. Temperature differences in a semiconductor material are used, between which a voltage builds up. The principle has been known for a long time from space travel, for example, but so far it has only remained a fixed idea in cars, as the output is hardly more than 200 watts.
Thanks to advances in the materials used for semiconductors, the value could possibly be increased fivefold in the foreseeable future, the developers estimate. And are happy to be able to reduce the energy loss even further when the engine is producing a lot of it. At 130 km / h, the recovered energy could be enough, together with the start-stop system, to cover the electricity needs of a 5-series BMW. In this way, fuel consumption could be reduced by around five percent. From today's perspective, however, the thermoelectric generator is more suitable for larger cars because of the space it requires. Series production can only be expected in a few years.
Little effective energy conversion
In order to generate one watt of electrical energy for the vehicle electrical system, the motor must provide two watts of mechanical energy. In order to improve this imbalance, BMW has long been planning to use solar systems in the vehicle roof. According to experts, today's photovoltaic modules are able to fully charge the starter battery under halfway favorable conditions. The power saved by the alternator is not insignificant, as charging with an additional 0.3 liters of fuel per 100 kilometers affects total consumption. Solar power could be used for heating or keeping engine oil or coolants warm and thus improve the cold start phase of the engine, which is known to consume a lot of fuel and generate a comparatively large amount of CO2 and other pollutants. The effects depend on the amount of heat captured.
According to BMW, there is also considerable potential in the further networking of on-board electronics, including navigation devices. The developers see this as an opportunity for future vehicles to act with more foresight.
With the help of the sensors that determine the vehicle condition, the camera recognition that provides information about the current traffic situation, radar that monitors the vehicle environment and the navigation system that classifies the respective geographical situation, an overtaking maneuver can be prepared, for example. The engine control could be influenced with such calculations in such a way that it converts the combustion from lean operation to a more homogeneous mixture and also adjusts the oil and coolant temperatures. Additional units such as the air conditioning system would be temporarily disconnected and the switching operations would be prepared. In this way the friction losses of the system could be reduced. The vehicle reacts much more spontaneously.
Before a traffic jam, the coolant temperature would also be automatically lowered, the air conditioning would be set to step-by-step traffic, and in a hybrid car the memory would be filled in order to cope with the slow travel in traffic jams as electrically as possible, i.e. fuel-saving.
The costs for all these measures should be kept within reasonable limits compared to other investments, because, with a few exceptions, no fundamentally new technology is required. However, the tax expense increases significantly. The corresponding software, it was said at BMW, is already being developed.
