Dual fuel knock mitigation technique through liquid state injection

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).