Effect of Compression Ratio on Cycle-by-Cycle Variations in a Natural Gas Direct Injection Engine

Abstract

Cycle-by-cycle variations of a natural gas direct-injection spark ignition engine at different compression ratios were investigated. The results show that the lean burn limit of the natural-gas direct injection engine can be extended to a larger overall excess air ratio compared with that of the homogeneous charge natural gas engine. The coefficient of variations (CoV) of indicated mean effective pressure decreases with the increase of compression ratio. However, CoV of indicated mean effective pressure is increased at high engine load when compression ratio is larger than 12. The cycle-by-cycle variations are more clearly demonstrated in CoV of indicated mean effective pressure rather than in CoV of cylinder peak pressure. Average values of flame development duration, main combustion duration, and total combustion duration are decreased and combustion is improved with increasing compression ratio. This is the reason for decreasing cycle-by-cycle variations in the natural gas direct-injection engine. Better interdependence exists between the indicated mean effective pressure and the flame development duration, as well as between the indicated mean effective pressure and late combustion duration. Cycle-by-cycle variations of the natural gas direct-injection engine are resulted from cycle-by-cycle variations in flame development duration and late combustion duration. This shows some difference to that of homogeneous charge natural gas engine, where cycle-by-cycle variations are mainly influenced by the variations in early flame development stage.

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

“…The situation is similar in HCCI engines where the CCV in IMEP also result mainly from variations in the initial stages of combustion. However, in direct-injection spark-ignition engines, it is found that CCV during the later combustion periods may also have strong influence on the cyclic pressure variations [44][45][46].…”

“…In their recent work, Zheng et al [45,46] performed experimental studies of combustion in a natural gas direct-injection spark-ignition engine. In particular, they [46] analyzed the effect of compression ratio on the CCV of IMEP and investigated the interdependency between the CCV of IMEP and flame development duration, main combustion duration and total combustion duration.…”

Spark Ignition Engine Combustion, Performance and Emission Products from Hydrous Ethanol and Its Blends with Gasoline

“…It was concluded that compression ratio was a key parameter for improving brake thermal efficiency when using hydrous ethanol as fuel [71]. Zheng et al [72] confirmed that CCV is lower with increased compression ratio, with the enhanced combustion characteristics. According to a study conducted by Young [73], there was 10% increase in power output for an identical fuel consumption and that a decrease in emissions from the engine could be achieved if the CCV could be reduced.…”