# Gain in Thermal Efficiency from Additional Expander Unit

In summary, by fitting a compact and efficient positive displacement additional expander unit to a Wankel gasoline engine, an increase in thermal efficiency of approximately 5-10% can be expected with the improved Atkinson Cycle.
If a Wankel gasoline engine was to be fitted with a compact and efficient positive displacement additional expander unit such that the normal exhaust from the engine was further expanded down to atmospheric pressure before being released to atmosphere, what gain in thermal efficiency could be expected ?
In principle an improved Atkinson Cycle would be achieved.
Assume that the adiabatic efficiency of the expander device is 75% and that no gas transfer losses are incurred; that the exhaust gas condition at the time when the exhaust port of the engine opens is 950 C and 5.5 bar absolute pressure; and that the engine operates only at a single speed and at full throttle as could be used, for example, to drive a generator in a Series Hybrid electric vehicle.

The improved Atkinson cycle would result in an increase in the thermal efficiency of approximately 5-10%. This is because the additional expansion of the exhaust gas allows for more of the energy in the exhaust to be converted into useful work, rather than being wasted as heat. Additionally, the increased compression ratio would also increase efficiency by reducing the amount of fuel needed to create the same power output.

## 1. What is "Gain in Thermal Efficiency from Additional Expander Unit"?

The "Gain in Thermal Efficiency from Additional Expander Unit" refers to the increase in efficiency of a thermal power plant when an additional expander unit is added to the system. This expander unit helps to extract more energy from the same amount of fuel, resulting in a higher thermal efficiency.

## 2. How does an additional expander unit improve thermal efficiency?

An additional expander unit works by expanding the exhaust gases from the primary turbine, which still contain a significant amount of energy, and using that energy to drive another turbine. This allows for more energy to be extracted from the same amount of fuel, resulting in a higher thermal efficiency.

## 3. What factors affect the potential gain in thermal efficiency from an additional expander unit?

The potential gain in thermal efficiency from an additional expander unit depends on various factors such as the type and size of the expander unit, the type of fuel used, the operating conditions of the power plant, and the efficiency of the primary turbine.

There can be some disadvantages to adding an additional expander unit, such as increased capital and maintenance costs, and the need for additional space in the power plant. Additionally, if the expander unit is not properly integrated into the system, it can lead to operational issues and decreased efficiency.

## 5. How can the gain in thermal efficiency from an additional expander unit be calculated?

The gain in thermal efficiency from an additional expander unit can be calculated by comparing the overall thermal efficiency of the power plant before and after the addition of the expander unit. This can be done by analyzing the energy input and output of the system and calculating the difference in thermal efficiency.

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