Investigation into the Relationship between Super-Knock and Misfires in an SI GDI Engine

Abstract

The super-knock poses new challenges for further increasing the power density of spark ignition (SI) engines. The critical factors and mechanism connecting regarding the occurrence of super-knock are still unclear. Misfire is a common phenomenon in SI engines that the mixture in cylinder is not ignited normally, which is often caused by spark plug failure. However, the effect of misfire on engine combustion has not been paid enough attention to, particularly regarding connection to super-knock. The paper presents the results of experimental investigation into the relationship between super-knock and misfires at low speed and full load conditions. In this work, a boosted gasoline direct injection (GDI) engine with an exhaust manifold integrated in the cylinder head was employed. Four piezoelectric pressure transducers were used to acquire the data of a pressure trace in cylinder. The spark plugs of four cylinders were controlled manually, of which the ignition system could be cut off as demanded. In particular, a piezoelectric pressure transducer was installed at the exhaust pipe before the turbocharger to capture the pressure traces in the exhaust pipe. The results illustrated that misfires in one cylinder would cause super-knock in the other cylinders as well as the cylinder of itself. After one cylinder misfired, the unburned mixture would burn in the exhaust pipe to produce oscillating waves. The abnormal pressure fluctuation in the exhaust pipe was strongly correlated with the occurrence of super-knock. The sharper the pressure fluctuation, the greater the intensity of knock in the power cylinder. The cylinder whose exhaust valve overlapped with the exhaust valve of the misfired cylinder was prone to super-knock.

The comparative performance study of the EF7 downsized engines; fuel economy besides CO2 reduction

“…Using modified inlet components design [19], developed TC such as Variable Geometric Turbines (VGT) [20] and twin-turbines [21], improved injection strategy [22], water injection [23], employing additives [24], combined [25] and alternative [26] fuels, Exhaust Gas Recirculation (EGR) [27], and electrified components [28] are considered as the some of these techniques. It is asserted that both fuel economy and 𝐶𝑂 2 production rate are noticeably improved during these efforts, but some challenging issues such as knock [29] and super-knock [30], Low-Speed Pre-Ignition (LSPI) [31], and weak performance especially at low-speed regions [32] are the main obstacles which researchers try to cope with them. Indeed, to achieve the ultra-emission reduction goal, the efforts lead to the usage of Compressed Natural Gas (CNG) as the fuel of downsized engines [33][34][35].…”