Using the waste heat from a car engine in a hybrid
The most efficient car engines of today have a thermal efficiency of 22%-25%. This is when all other factors are optimized. In reality, most vehicles barely manage to achieve an efficiency of 20%. A large chunk of the rest of the energy escapes through the exhaust. There is a growing realization that this energy can be reused, which would increase the efficiency of most vehicles. It would entail converting it into electric energy, which can be stored in batteries. Later on, it can be used to power the vehicle in a hybrid configuration.
Systems for Heat Recovery
The Rankine cycle system vaporizes water using a steam generator in the exhaust pipe. Owing to this heating by the hot exhaust gases, the fluid turns into steam, which drives the expander of the Rankine engine. The expander will be linked to an alternator that generates electricity. Scientists at Loughborough University and the University of Sussex have calculated that waste heat from light vehicle engines in the steam power cycle could lead to fuel economy advantages of 6.3%-31.7%. This efficiency can be achieved within normal operating pressures.
Honda was amongst the first companies to test this system in 2008. They used the Honda Stream as a test bed. During initial tests, the car, when moving at a constant 100km/h was able to improve thermal efficiency by 3.8%.
The Turbosteamer is a term coined by BMW to describe their combined cycle engine. Waste heat from the car engine is used to generate steam for a steam engine that would produce power for the car. The device was fixed to the cooling and exhaust systems. It collects heat power from the exhaust and radiator and uses a steam turbine to direct power to the crankshaft. This leads to about 14hp of torque at its peak; it represents about a 15% gain in efficiency. Unfortunately, the system has never been installed in any of the BMW cars except for a prototype BMW X6.
The MGHU-H stands for Motor Generator Unit-Heat, which is a system that can be found in racing cars, especially the formula 1 car. The system is connected to the turbocharger and the compressor. It captures heat coming from the exhaust gases, turning it into electric energy. It also acts as the control system for the turbo by slowing or speeding it up, which depends on the requirements of each driver. With this system, F1 cars usually have almost no turbo lag.
Refrigeration Units in Trucks
An area that could utilize recovered heat from the engine block is the refrigeration unit in trucks. A company working on this in the UK is Clean Power Technologies. It has a set up where heat from the engine exhaust is directed to a steam accumulator. Water can then be heated up to 360C or more, which creates steam that can provide energy. The company planned to use this steam energy to generate power that will run a refrigeration unit; they first released a prototype in 2008. This could lead to serious savings if the technology were to receive mass adoption. It has been calculated that, currently, trucks in the UK spend about £7,000 a year to power their refrigeration units. The company does not just look at land-based vehicles. It also aims to generate power with engines found on marine vessels. Their engines operate in much the same way as land-based cars.
One of the most promising technologies is thermoelectric generators. They convert the temperature difference into power. This technology was first discovered in 1821. It was discovered that the temperature difference between material causes the flow of charge carriers. This flow of charge carriers leads to a voltage difference.
However, it is only in modern times that the use of nanotechnology is making it possible to optimize the devices. In this device, heat enters the first part of the module and then travels through a semiconductor to the cooler part. The motion of electrons in the semiconductor is then extracted as power.
The problem is that atomic vibrations leak heat from the hot to the cool side. However, with new technology, heat leakage can be reduced by about 60 percent. The US Department of Energy has sunk millions of dollars in this technology in the past. With this technology, a car’s efficiency can be boosted by about 5 percent. This technology was heavily researched in the 50s. It ended up being used in refrigeration and sensors. However, it has never received any large-scale application in the motor vehicle industry. The main problem that the industry has faced is that the materials equalize heat too fast. As a result, they become inefficient quite quickly. One of the companies producing commercial TEGs is GMZ. They utilize Half-Heusler materials. The alloy allows better stability at high temperature.
Waste Heat Recovery in Hybrids
Any car could benefit from the generation of electricity from waste heat in the engine. However, the optimal efficiency is achieved in hybrid cars. These vehicles have an electric battery where power is stored to power the car later. For one, it ensures no money is spent charging the batteries. It also ensures that the amount of time needed to recharge batteries is reduced.
The world’s fossil fuel reserves are running low. One way this could play out is that it leads to more hostility over the fight for dwindling energy resources. It could also mean that fuel prices become too high, which could have a negative effect on economies around the world.
One of the best ways to avoid these issues is the use of heat recovery technology in commercial vehicles and later on personal cars. It will ensure that there is less pollution in the environment. Besides that, it will reduce the risk of a scramble for the dwindling fossil fuel reserves. It is important that these technologies be developed now before the world runs low on fossils or it chokes on the dangerous emissions from fossil fuels.