Feasibility and performance analysis of cylinder deactivation for a heavy-duty CNG engine

Engine emissions regulations are becoming increasingly stringent due to the higher concern and visible changes in global warming and people health. Thus, new studies and new technologies are becoming more and more relevant as there is a need to respect these important rules to preserve the safety of people and the world. In this perspective, alternative fuels are useful to decrease the content of net carbon dioxide and pollutants emitted in the environment by exploiting their composition and production. Engines powered by natural gas represent an important step towards the net-zero greenhouse gas emissions EU targets. Natural gas guarantees lower CO2 emissions per units of energy compared to conventional diesel and gasoline engines; it has a higher octane number which allows for higher compression ratios, hence it has a higher thermal efficiency compared to gasoline engines. The interest is high especially in the heavy-duty sector as it can be a substitute of diesel engines because it ensures the same performance while its usage would be more convenient due to the lower market price of natural gas. At the same time, new technologies such as cylinder deactivation can be useful to directly reduce the fuel consumption and CO2 and pollutants emissions; it can also be employed to increase the in-cylinder temperatures ensuring increased catalyst conversion efficiency. The aim of this thesis is to study the application of cylinder deactivation on a six-cylinders heavy-duty compressed natural gas SI engine, by exploiting 1D modelling in GT-Suite. It has been carried out in collaboration with the Institute of Sciences and Technologies for Sustainable Energy and Mobility (STEMS) of the Italian National Research Council in Naples. The starting point of this work is an already existing 1D model of this engine, calibrated from experimental data. The study has been divided in two main sections: steady-state and transient conditions. In the first part, 25 operating points from the engine workplan have been analysed, sweeping between different speeds and loads conditions. The aim of this section is studying the feasibility of cylinder deactivation and the best solutions in order to apply it. Several configurations have been studied and the choice has been to implement a fixed three-cylinders deactivation applied by recirculating exhaust gas in the three deactivated cylinders, guaranteeing a simple deactivation mechanism. After having defined the configuration and functioning, the transient analysis has been performed: the model has been run in some significant portions of the World Harmonized Transient Cycle (WHTC) to study the advantages in a real working cycle. This highlighted the expected fuel consumption benefit, and the temperature increase that would allow the after-treatment system to work with higher efficiency.