 Welcome back Mechanical AI. Did you know that Declare's Auto devises an engine based on the Auto Cycle which was twice as efficient as other cycles of their time? This makes us wonder, what is the Auto Cycle? Before we jump in, check out the previous part of this series to learn about what cogeneration is. Now, there are certain assumptions for AI that we need to consider before studying the Auto Cycle. It starts with the working fluid which is air. It continuously circulates in a closed cycle. Air is considered an ideal gas. All the processes in ideal power cycles are internally reversible. Combustion process is modeled by a heat addition process from an external source. The exhaust process is modeled by a heat rejection process that restores the working fluid air at its initial state. And finally, specific heats are assumed to be constant at 25 degree Celsius for air. Now, we'll look at the Auto Cycle using processes. Process 0, a mass of air is drawn into the piston or cylinder arrangement at constant pressure. Process 1 is an adiabatic compression of the charge as the piston moves from bottom dead center to the top dead center. Process 2 to 3 is a constant volume heat transfer to the working gas from an external source while the piston is at the top dead center. This process is intended to represent the ignition of fuel-air mixture and the subsequent rapid burning. Process 3 to 4 is an adiabatic expansion also called the power stroke. Process 4 to 1 completes the cycle by a constant volume process in which heat is rejected from air while the piston is at the bottom dead center. In the final process 1 to 0, the mass of air is released to the atmosphere in a constant pressure process. Hence, we first saw what the air cycle assumptions are and then saw what the auto cycle is.