https://www.um.edu.mt/library/oar/handle/123456789/930 Fri, 24 Apr 2026 18:57:17 GMT 2026-04-24T18:57:17Z https://www.um.edu.mt/library/oar/handle/123456789/145777 Title: Dual fuel knock mitigation technique through liquid state injection Authors: Fenech, Andrew; Saliba, Anthony Theodore; Farrugia, Mario Abstract: Dual-fuel engines allow the use of alternative fuels such as Liquified Natural Gas (LNG). Using LNG as the main energy source and a smaller quantity of diesel (to initiate combustion) offers the benefit of decreased emissions. The reduction of emissions is mostly due to the gaseous fuel’s better ability to burn more effectively. The gaseous fuels (e.g. methane CH4) has a lower carbon to hydrogen ratio than diesel and therefore less CO2 is produced. Particulate matter typically generated with diesel combustion is also greatly reduced. The use of dual fuel is however impacted by an operational phenomenon referred to as engine knock which limits the operational window of the engine. This knocking problem is accentuated during transients. The objective of this paper is to explore liquid state injection of LNG/propane. A small quantity of pressurized LNG/propane is injected into the airstream to lower the temperature of the charge air through the latent heat of evaporation of the LNG/propane. This liquid state injection is intended to lower the knock propensity especially during load increase transients where fuel is increased before the mass air flow has picked up (due to turbo lag). Sun, 01 Mar 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145777 2026-03-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145754 Title: Liquefied petroleum gas (LPG) transferring unit Authors: Farrugia, Mario; Briffa, Andrew; Fenech, Andrew; Saliba, Anthony Theodore Abstract: Liquefied Petroleum Gas (LPG) is a relatively widespread fuel used in a variety of applications such as cooking, transport and also industrial applications. LPG is a broad term, since its composition can vary but it is mostly composed of propane and butane or a mix of propane and butane. The convenience of LPG exists due to its physical properties which allow it to be contained in liquid form at room temperature and reasonable pressures presenting good energy density. The storage pressure is useful to deliver the fuel to burners. LPG also burns cleanly due to its chemical composition and efficient combustion. However, LPG use is hindered by the fact that it cannot be transferred easily from one container to another and therefore typically the LPG bottle/cylinder will be replaced, or filling has to be done at an industrial facility. This paper presents a setup designed, built, tested and used at the University of Malta that facilitated the filling of LPG at the thermodynamics laboratory thus making LPG usage much more convenient for our testing needs associated with engines. Wed, 01 Jan 2025 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145754 2025-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145753 Title: The use of lower or higher heating value, heat release rate and heat loss in internal combustion engines Authors: Saliba, Anthony Theodore; Farrugia, Mario Abstract: The heat release rate in internal combustion engines obtained from in-cylinder pressure data is a fundamental method to analyse the combustion characteristics of engines. As the measured in-cylinder pressure is lower than the pressure in the absence of heat loss to the walls, the methodology typically leads to the apparent rate of heat release as the heat loss to the cylinder walls cannot be segregated. Heat loss can then be inferred by reference to the chemical fuel energy expected to be released by the fuel. Typically, in engine thermodynamic analysis, the lower heating value is used to determine the energy released by the fuel. However, in this article, we argue that when detailed comparison with validated combustion modelling was done, it was concluded that the higher heating value is the more appropriate calorific value. In this research, the analysis of heat release rate and its determination using the first law of thermodynamics with constant ratio of specific heats γ and also varying γ is discussed. It was noted that the use of the “3rd term” (term due to the dγ/dϑ) in the heat release rate is advisable as it gives a more reasonable heat loss even in the compression stroke. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145753 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145752 Title: Combustion characterization and heat loss determination through experimental investigation of hydrogen internal combustion engine Authors: Fenech, Andrew; Portelli, Stefan; Pipitone, Emiliano; Farrugia, Mario Abstract: Hydrogen combustion is known to be fast compared to traditional hydrocarbon fuels. The fast combustion leads to a higher thermal efficiency. In this research a 600 cc single cylinder hydrogen engine was tested at 1250 rpm, lambda = 2 and 3, and three load levels (load was represented by Manifold Absolute Pressure (MAP); MAPs tested were 75, 95 and 120 kPa) and compared to operation with gasoline and propane. The fast burn duration (Mass Fraction Burnt MFB10% to MFB90%) and the MFB 50% were determined and analyzed. The hydrogen MFB50% location for Minimum Timing for Best Torque (MBT) was found to occur at around the typical 8 Crank Angle Degrees (CADs) After Top Dead Center (ATDC). Measurements of ignition delay based on the fast data direct measurement of spark ignition coil current drop to the change in polarity of net heat release are presented. With shifts towards direct injection and higher injection pressures, consideration was given to the hydrogen pressurization penalty, where it was calculated that pressurizing hydrogen to 100 bar at the flow required for lambda = 2 operation is 2.3 bar, i.e., higher than the Friction MeanEffective Pressure (FMEP)! Furthermore, hydrogen is widely cited to have a higher heat loss than typical hydrocarbon fuels. In this paper, detailed analyses at lambda 2 and lambda 3 showed that hydrogen in fact has lower heat losses. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145752 2026-01-01T00:00:00Z