Effect of Fuel Injection Timing Relative to Ignition Timing on the Natural-Gas Direct-Injection Combustion

Abstract

The effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine (RCM). The ignition timing was fixed at 80 ms after the compression start. When the injection timing was relatively early (injection start at 60 ms), the heat release pattern showed a slower burn in the initial stage and a faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively late (injection start at 75 ms), the heat release rate showed a faster burn in the initial stage and a slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realized at the injection end timing of 80 ms (the same timing as the ignition timing) over a wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet are considered to cause this behavior. Early injection leads to longer duration of the initial combustion, whereas late injection leads to a longer duration of the late combustion. Early injection showed relatively lower CO concentration in the combustion products while late injection gave relatively lower NOx. It was suggested that early injection leads to combustion with weaker stratification, and late injection leads to combustion with stronger stratification. Combustion efficiency was kept at a high value over a wide range of equivalence ratio.

Characteristics of direct injection combustion fuelled by natural gas–hydrogen mixtures using a constant volume vessel

“…The deviation for turbulent combustion by this treatment is small due to the short combustion duration [30]. Thus, the rate of pressure rise is proportional to the rate of heat release and the information of heat release rate can be reflected by the information of pressure rise rate.…”

“…9 and 10, respectively. In this paper, the initial combustion duration is defined as the time interval from ignition timing to 10% of pressure rise due to combustion, and the main combustion duration is defined as the time interval from 10% to 90% of pressure rise due to combustion [30]. Similar to peak pressure and maximum rate of pressure rise, in the case of stoichiometric mixture combustion, the initial combustion duration and main combustion duration are slightly influenced by the hydrogen addition, the fast burning velocity at the stoichiometric equivalence ratio contributes to such phenomenon.…”

Dynamics of cycle-to-cycle variations in a natural gas direct-injection spark-ignition engine

“…Lean mixtures of alternative fuels such as natural gas, biofuels and fuel-blends, with operational modes such as direct injection (DI) and homogeneous charge compression ignition (HCCI) have been realized in recent years, with improved performance over the conventional gasoline and diesel engines [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. However, internal combustion engines suffer from cycle-to-cycle variations (CCV) in combustion variables such as pressure, and these cyclic variations may become severe under lean burn conditions or for highly dilute mixtures with exhaust gas recirculation (EGR) [16][17][18][19][20].…”

Development of an Experimental Database and Kinetic Models for Surrogate Diesel Fuels

“…There are several experimental apparatuses that may be appropriate to evaluate these targets. For example, rapid compression machines and shock tubes have been extensively used to measure the first and second stage heat-release timings and amounts [146,147]. These apparatuses have been routinely operated at 6 MPa pressure [97,98] and capabilities up to 60 MPa have been demonstrated [98].…”