Abstract
The Inspiration of this work is a novel engine concept, in which the combustion process is performed homogeneously in a porous reactor. This engine concept has high potential to achieve an ultra-low emission level and increase the engine efficiency. Homogeneous combustion in porous reactors has already proven near zero exhaust emissions under steady state conditions. However, under engine-relevant conditions, this technology has rarely been investigated. For an internal combustion engine application, the time scale of mixture formation and combustion process is crucial. Thus, its investigation is the main objective of the present research. Fluid mechanical and thermodynamic conditions in porous reactors differ considerably from conventional, free volume systems. Therefore these processes were investigated fundamentally as well as all associated thermo-dynamical and process models. This is the first reported attempt to investigate these processes in porous reactors under engine-relevant conditions.The investigation on mixture formation in porous reactors showed that the multi jet-splitting effect leads to a quick three-dimensional distribution of the fuel in space. Furthermore, in case of a hot porous reactor, the liquid fuel is vaporised very quickly. The heat release process is investigated in different porous reactors and under free volume conditions ( no reactor applied), as reference case. It is shown, that in case of porous reactors the pressure and temperature changes during the heat release process are clearly lowered as compared to free volume conditions. This is an effect of heat transfer and heat accumulation in the reactor's solid phase, which also reflects the reaction rates. The results show that at low initial temperatures and/ or low initial pressures the reaction rate is higher in porous reactors. However, at high initial temperatures and pressures the reaction rate is reduced in porous reactors as compared to the free volume case. This has the favourable effect of accelerating the combustion process at low loads and to prevent high mechanical stresses at high loads.
The present investigation in addition shows that the time scales of mixture formation and combustion process in porous reactors can be in the order of a few milliseconds only. This is similar to the free volume case or even shorter. Additionally, it is shown that the heat release rates are high enough for engine application. However, in contrast to free volume conditions the heat release rate in case of porous reactors does not further increase at high loads. The results indicate a possible extension of homogeneous combustion to a full range of engine load and rotational speed when performed in porous reactors.
| Date of Award | Oct 2014 |
|---|---|
| Original language | English |
| Supervisor | Talal Maksoud (Supervisor) |