gtr11ECETRANS180Add.11Appendix 2 page 5 I. MOTIVATION FOR THE GUIDANCE DOCUMENT 1. This guidance document is a support document to the global technical regulation (gtr) onUN GTR No. 4 - Test procedure for compression-nition (C.I.) engines and positive-nition (P.I.) engines fuelled with natural gas (NG) or liquefied petroleum gas (LPG) with regard to