M.Sc Thesis


M.Sc StudentKarsenty Kadmiel
SubjectA Diesel Engine with a Catalytic Piston Surface for
Small Aircrafts Propulsion at High Altitudes -
Theoretical Study
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Eran Sher
ASSOCIATE PROF. Leonid Tartakovsky
Full Thesis textFull thesis text - English Version


Abstract

There has recently been a large increase in development activities of remotely-controlled and autonomous Miniature Aerial Vehicles (MAV). Military, scientific, law enforcement and mapping usage are among the important potential applications that motivate this effort. Among the more challenging limiting factors of the MAV development are the engine thermal efficiency and its performance degradation at high altitudes.

In this work we propose a unique method to extend the upper-limit altitude with no noticeable extra weight to the device. We propose a special in-cylinder steam reforming approach to significantly increase the engine efficiency at high altitudes, thus enabling engine operation at higher altitudes with a negligible weight penalty. The improvement in the engine performance at high altitude is attributed to the unique method of internal heat recovery (in-cylinder steam reforming) in which a wider flammability and higher burning velocity are achievable. In the present research we analyze the effect of the in-cylinder steam reforming process on the engine performance at high altitudes. The analysis is based on a rigorous mathematical model of the various processes that occur inside the cylinder during a complete cycle. The model equations are solved by using the commercial software GT-Power by Gamma Technologies. The results show that by the employment of the internal steam reforming concept in internal combustion engines (in either 2- or 4-stroke engines), it is possible to increase the indicated efficiency and the engine brake power and therefore decrease the fuel consumption. Moreover, due to higher in-cylinder pressure with no increase in temperature, the cycle effectiveness is higher while the amount of NOx emission remains the same. Preliminary comparative tests of previous studies showed an indicated efficiency increase of around 10% and a corresponding decrease in the brake specific fuel consumption (BSFC) of about 8%. In our work, we show an increase of up to 6% in the indicated efficiency and a corresponding decrease of up to 7% in the BSFC, at sea level, depending on the ratio between the moles of the diesel fuel to the moles of the diesel and methanol. This improvement is achieved through changing the volumetric efficiency. With higher volumetric efficiency, a higher amount of air enters the cylinder. As a result, it is possible to burn more fuel and therefore to achieve an increased work per cycle and thus increased power, for the same engine speed. We show that, at different altitudes, by using in-cylinder steam reforming, the BSFC and the brake power can be improved up to 9% and 8% respectively, at every altitude examined. Although the efficiency improvement decreases for higher altitudes (relative to sea level), the efficiency with our special design is higher in most cases by 1−4% (at constant lambda value) and by 1−13% (at constant brake power) in comparison to the conventional design. The steam reforming helps to extend the upper-limit altitude of the UAV by about 5,000 feet, in addition to significant increase in the efficiency. Therefore, the steam reforming enables engine operation at higher altitudes with a negligible weight penalty.