Effects of applying EGR with split injection strategy on combustion performance and knock resistance in a spark assisted compression ignition (SACI) engine

Abstract

Spark assisted compression ignition (SACI) is a proven method for extending the load range and controlling the combustion phase of homogeneous charge compression ignition (HCCI) while maintaining high thermal efficiency. However, the occurrence of abnormal combustion, such as knock, limits the improvement of efficiency in SACI combustion. In this study, the effects of a coupling strategy, which combines internal/external exhaust gas recirculation (i & e-EGR) and split injection, on knock suppression in SACI mode were investigated in a high-compression-ratio, single-cylinder gasoline engine with a fully variable valve system. During the experiment, the mass of intake air remained constant while e-EGR was added. The results show that the coupling strategy combines the advantages of e-EGR and split injection, providing an effective method for resisting knock and improving engine efficiency. The results also demonstrate that applying e-EGR to SACI combustion significantly decreases the knock intensity by effectively reducing the in-cylinder temperature. In addition, the effect of split injection on knock suppression is related to the initial in-cylinder temperature and fuel stratification. With high initial in-cylinder temperature, the relationship between knock probability and split injection timing is non-monotonic. However, with low initial in-cylinder temperature, the capacity of resisting knock monotonically increases with the delay of secondary injection timing.

An applicable approach to mitigate pressure rise rate in an HCCI engine with negative valve overlap

“…In other words, thermodynamic conditions and chemical composition of the combustible mixture at intake valve closing (IVC) define the timing and duration of subsequent combustion process. Some additional controllability after IVC can, however, be introduced by means of direct injection (DI) of fuel, providing mixture stratification [11,12], or by socalled spark assist technology [9,13].…”

Combustion development in a gasoline-fueled spark ignition–controlled auto-ignition engine operated at different spark timings and intake air temperatures

“…When considering the mean value of MFBtrans, it decreases by about 3% at 473 K Tintake with advancing ST. However, advancing ST has increasing trends in the mean values of MFBtrans at Tintake of 498 and 523 K. 41 These may be explained with that decreasing compression heat addition to initial thermal state at the onset of combustion due to advancing ST requires a higher percentage of MFB consumed by the flame propagation. It can also be stated that the advanced ST from −30 °CA to −40 °CA has a little effect on MFBtrans 46 at 523 K Tintake that is already sufficient to initiate the combustion process at early stage relative to 473 and 498 K.…”

“…In the study, the transition point was identified using the first maximum point of the second derivate of HRR ( d 2 HRR / d θ 2 ) . 41,42 A typical HRR curve of SICAI combustion has an inflection point ( T ) which brings about the maximum point on HRR″ curve, as shown in Figure 3. Thus, MFB of flame propagation (SI combustion) is also determined by the CAtrans point.…”

In-Cylinder Oxygen Concentration Estimation Based on Virtual Measurement and Data Fusion Algorithm for Turbocharged Diesel Engines

“…However, these technologies operate in a limited range of engine conditions closing to the combustion stability boundaries [2][3][4]. In this case, combustion failure such as misfire [5,6] and knock [7,8] happen under slightly mismatching of in-cylinder conditions. To achieve promising performance, advanced combustion control strategies are demanded.…”