On-board fuel tailoring with a novel catalytic evaporator for HCCI combustion

The following study describes an on-board fuel tailoring process based on a novel and compact catalytic fuel evaporator, capable of optimizing Homogenous Charge Compression Ignition (HCCI) combustion. Evaporation tests with conventional diesel were performed revealing a significant amount of long-chain alkane cracking. As a consequence of these cracking reactions, the presented experiments demonstrate that the produced fuel vapor has altered combustion properties as compared to the feeding diesel stream. Further tests using a constant volume chamber at 30 bar, over the temperature range 500 to 1120 K, indicated that ignition delay time and auto ignition temperature of this fuel vapor can be shifted from diesel to gasoline. Thus, by performing dynamic on-board adjustment of the fuel properties, it is possible therefore to increase HCCI combustion to high loads. Complimentary to experiments with the fuel evaporator, GT-Power Simulations were also performed, with the aim to predict the boundary conditions to be used in subsequent engine tests. Engine tests were performed with the evaporator device mounted directly at the intake manifold of a one cylinder diesel research-engine, acting as a port injection. Compared to conventional diesel operation, a considerable reduction of NOx was observed, whilst Particulate Matter (PM) emissions were below the limit of detection. Significantly, the presented work demonstrates that ingnition timing is also controllable. By adjusting the fuel vapor composition, the combustion phase can be shifted without Exhaust Gas Recirculation (EGR) to the After Top Dead Center (ATDC).