Weird, a little research on google, indicates that natural gas doesn’t like spark ignition at a compression ratio above 11.5:1.
I would not have guessed that..
At Diesel compression ratios the peak cylinder pressure is so high that the voltage to initiate a spark discharge is so great and the amps so high spark plug life is well almost none existent, There has been some research work on using lasers to solve this problem, or as is done in large stationary NG engines of the megawatt class use plasma jet ignition but in the medium speed market i would think plasma jet would be horribly expensive to implement at a firing rate of +1600 hz. The simple solution is to “pilot” inject some diesel right before TDC this pilot fuel lights off and kicks off the stoichiometric NG gas burn, The good thing about NG is no particulates and you can go to stoichiometric mixing rates skip the fancy DPF filters and DOC + NOx after treatments using a simple 3 way conventional catalytic converter is possible if you run stotomietical mixtures.