Study on cycle-by-cycle variations of combustion in a natural-gas direct-injection engine

Abstract

In this paper, the cycle-by-cycle variations of a compressed-natural-gas (CNG) direct-injection (DI) engine were investigated. The results show that the CNG DI engine has a better lean burn capability, and misfire cycles and partial burn cycles exist when the engine operates at small equivalence ratio (>0.4). Meanwhile, the indicated mean effective pressure (IMEP) has a low value, and the high value of the coefficient of variation in the IMEP is presented in comparison with those operating at a high equivalence ratio. Cycles with a high maximum cylinder pressure correspond to the cycles of fast burning, and parameter interdependence is observed between the maximum cylinder gas pressure and its corresponding crank angle, between the maximum rate of pressure rise and its corresponding crank angle, and between the maximum cylinder pressure and the indicated mean effective pressure. Better parameter interdependence exists between the maximum cylinder pressure and the flame- developing period, between the maximum cylinder pressure and the rapid-burning period, and between the accumulated heat release amount per cycle and the indicated mean effective pressure. A small variation in the flame-developing duration will lead to a large variation in the rapid-burning duration under lean mixture combustion; the slow flame propagation speed of the lean mixture combustion is considered to lead to this phenomenon.

Effects of Fuel Injection Pressure on Combustion and Emission Characteristics under Low Speed Conditions in a Diesel Engine Fueled with Palm Oil Biodiesel

“…To verify the combustion stability of the diesel engine operation at idle using each test fuel, the coefficient of variation (COV) for the indicated mean effective pressure was used, which is defined as [12,13,29]:…”

Characterization of cycle-to-cycle variations in a natural gas spark ignition engine

“…Recently it also has been studied in homogeneous charge compression ignition (HCCI) engine processes [14], compression ignition engines [15] and also by using CFD simulations [16]. A traditional [17][18][19][20][21][22] estimator of the cycle-to-cycle variation is the Coefficient of Variation in Indicated Mean Pressure, COV IMEP . In this paper, the authors propose complementary considering the variation of the mass fraction burning rate of each individual cycle to characterize cyclic variation, as explained later (Fig.…”

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

“…It is important to understand the nature and dynamics of the CCV in order to develop effective strategies for controlling them [25,26]. Several investigators have examined the CCV in spark ignition, compression ignition, and HCCI engines [27][28][29][30][31][32][33][34][35][36][37][38]. For the conventional spark-ignition engine, the studies revealed that variations occurring mainly in the early combustion stage influenced the CCV of indicated mean effective pressure (IMEP), and any factor which can increase the burning velocity of the mixture will lead to a reduction of the CCV [39][40][41][42][43].…”