Algorithm for Determining the Knock Resistance of LNG

This paper reports the development of a next-generation algorithm to calculate the knock resistance for LNG compositions. This so-called PKI Methane Number is developed and tested for a lean-burn, medium-BMEP gas engine. The algorithm itself is a polynomial equation based on thousands of simulations performed using an experimentally verified engine knock model. Comparison of the PKI MN calculated using the gas-input-only algorithm and measurements on the test engine show very good agreement. A comparison with two existing methods for calculating the methane number (AVL and MWM Method as defined in EN 16726) with experimental engine data show reasonable agreement with predictions using AVL method but substantial differences with predictions from MWM method are observed. Additionally, the current methods such as AVL and MWM need a dedicated solver to calculate the methane number. In contrast, the algorithm described here is a polynomial equation that is very easy to implement in gas composition sensors for fast real-time methane number calculations. This opens possibilities for smart-phone methane number calculation during bunkering and fuel-adaptive control systems that could optimize engine performance for a broad range of fuel compositions. Furthermore, given the experimentally verified reliability and ease of implementation of the PKI MN algorithm, we assert that it is an excellent, open-source candidate for international standards for specifying the knock resistance of LNG.