Thermodynamics Review Problems for Mechanical Engineering Students | Series 19: Diesel Cycle

For this review problem, the very first thing to obtain is the temperature at the end of isentropic compression which is T2 and it can be obtained using the temperature and volume relation relations during isentropic compression and thankfully we are provided with the compression ratio that is equal to 15 and by using the relation, we’ve found out that T2 is equal to 889.21°K. Second thing to obtain is the temperature at the end of heat addition process which is T3 and it can be obtained using the temperature and volume relation at heat addition process for which there is a cut-off ratio (rc) for which it is provided in the review problem and by using the relation, we’ve found out that T3 is equal to 2667.63°K. If you’ve noticed in the computation below, T2 is also the temperature at the beginning of heat addition process. Next thing to obtain is the heat that is being added during the heat addition process, this time around we will be using the specific heat capacity at constant pressure (cp) and by doing so, we’ve found out that QA is equal to 1778.42 kJ/kgm, do take note that cp of air is equal to 1 kJ/kgm/°K. Next thing to obtain is the cycle efficiency of the engine and it can be obtain by using the provided rk and rc. And by using the shortcut formula, we’ve found out that the engine is 0.5581 or 55.81 % efficient. Finally, we can now obtain the work of the engine and we can do that by simply multiplying the efficiency (e) and heat that is being added (QA) to the cycle. By doing so, we’ve found out that the work that is being done by the engine is equal to 992.54 kJ/kgm.