Experimental study of hydrogen combustion concepts using a heavy-duty single-cylinder setup : Comparison of Port Fuel Injection with Spark Ignition and High Pressure Direct Injection

In this work, several main combustion characteristic of PFI SI and HPDItm have been experimentally evaluated using the same singel-cylinder 1.8L heavy-duty research engine platform. The presented work considers fixed speed operation, wihtout the use of exhaust gas recirculation, primarily with stationair power generation in mind. The PFI SI concept is shown to have high protential for low NOx operation at medium to high load. The available load range for low NOx is mainly limited by the occurence of engine knock and available boost pressure. First results using an in-cylinder optical sensor show that the in-cylinder mixture is not necessarily homomgeneous at spark timing, even for port fuel injection. This inhomogeneity affects flame propagation and knock tendency. With the use of water injection into the intake manifold, high loads in excess of 24 bar have been achieved for the PFI SI concept. This, however, comes at the expense of increased engine-out NOx. The HPDI combustion concept clearly outperfomrs the PFI SI concept regarding miximium efficiency with appr. 7%-point higher observed net indicated efficiencies. High engine loads can be achieved with conventional boost pressures and bast CI engine combustion chamber hardware. For the HPDI concept, main parameter for optimizing the efficiency - NOx trade-off are the hydrogen main injection timing (i.e. combustion phasing) and the hydrogen rail pressure. Other parameters, such as the boost pressure (global excess-air ration) or pilot - hydrogen injection separation duration are found to have less impact. NOx eminissions for the HPDI concept are significantly higher, especially when targeting highest efficiency, and requires the use of an exhaust gas aftertreatment system.