Characteristics of Lean and Stoichiometric Combustion of Compressed Natural Gas in a Direct Injection Engine

Abstract

This paper discusses the combustion characteristics of CNG under lean and stochiometric conditions in a direct injection engine. The experiments were carried out on a dedicated CNG-Direct Injection engine with 14:1 compression ratio. Combustion characteristics of CNG have been investigated on various injection timings. Injection timing of the fuel injection timing had significant effects on the engine performance, combustion and emissions. The effects became more significant when injection timing was retarded. Injection timing was set after the closing of intake valve and experiments are conducted at 0% and 50% load conditions. Lean stratified operation experiences faster combustion compared to that of stochiometric. In lean stratified operation, there were fast burn rates at the initial stage and slower burning at the later stage. Whereas in stochiometric conditions there is a slightly slower burn at the initial stage and a moderately faster burn at the later stage. The faster initial combustion in lean stratified operation might be due to rapid burn of the initial mixture due to higher turbulence, while a slower burn in the later stage due to diffusion. In contrary to that in stochiometric operations the initial burn is slightly slower, due to moderately strong turbulence and a faster burn due to moderately proceeding mixture. Thus the main effect of fuel injection timing can be explained by the fuel air mixing and the turbulence produced.

Experimental study of pre-chamber jet ignition in a rapid compression machine and single-cylinder natural gas engine

“…8–11 Lean-burn is a combustion strategy widely adopted in NG engines due to its high thermal efficiency. 12 However, with the implementation of the sixth phase emission regulations, it will be difficult for the current lean-burn NG engines to meet the standards without expensive after-treatment systems, such as selective catalyst reduction (SCR), 13 or the challengeable ultra-lean-burn will have been realized. Stoichiometric combustion is a more effective and low-cost pathway to meet emission standards using a three-way catalyst (TWC), which was expected to be the more possible and feasible route for the sixth phase emission regulations.…”