Study of High Load Operation Limit Expansion for Gasoline Compression Ignition Engines

Abstract

In this research, combustion characteristics of gasoline compression ignition engines have been analyzed numerically and experimentally with the aim of expanding the high load operation limit. The mechanism limiting high load operation under homogeneous charge compression ignition (HCCI) combustion was clarified. It was confirmed that retarding the combustion timing from top dead center (TDC) is an effective way to prevent knocking. However, with retarded combustion, combustion timing is substantially influenced by cycle-to-cycle variation of in-cylinder conditions. Therefore, an ignition timing control method is required to achieve stable retarded combustion. Using numerical analysis, it was found that ignition timing control could be achieved by creating a fuel-rich zone at the center of the cylinder. The fuel-rich zone works as an ignition source to ignite the surrounding fuel-lean zone. In this way, combustion consists of two separate auto-ignitions and is thus called two-step combustion. In the simulation, the high load operation limit was expanded using two-step combustion. An engine system identical to a direct-injection gasoline (DIG) engine was then used to demonstrate two-step combustion experimentally. An air-fuel distribution was created by splitting fuel injection into first and second injections. The spark plug was used to ignite the first combustion. This combustion process might better be called spark-ignited compression ignition combustion (SI-CI combustion). Using the spark plug, stable two-step combustion was achieved, thereby demonstrating a means of expanding the operation limit of gasoline compression ignition engines toward a higher load range.

Study of the engine configuration effect on the maximum achievable load in CAI using water injection

“…Some of these approaches are well known, like EGR introduction, 12,13 charge stratification, 14 whereas others more specialized for CAI combustion, as for instance: fuel injection adapted strategies, valve train modifications or fuel composition adaptations. [15][16][17][18][19] In this work, the selected approach to overcome these limitations is based on the introduction of reaction suppressors within the charge in order to get a better control of the charge reactivity, thus optimizing the combustion process.…”

“…Some of these approaches are well known, like EGR introduction, 12,13 charge stratification, 14 whereas others more specialized for CAI combustion, as for instance: fuel injection adapted strategies, valve train modifications or fuel composition adaptations. 15–19…”

An analytical method for reducing combustion instability in homogeneous charge compression ignition engines through cycle-to-cycle control

“…In addition, retained exhaust occupies volume in the cylinder and displaces what would otherwise be fresh intake air, thus limiting the power capabilities of the engine. A method that can be used to increase the high-load capabilities of HCCI engines is to phase combustion at later engine crank angles, 1 which can be achieved in recompression HCCI by retarding the exhaust valve closing angle and retaining less exhaust in the cylinder, delaying the angle at which combustion begins. However, Wagner et al 2 and Shahbakhti and Koch 3 found that there is a significant increase in cyclic variation in indicated mean effective pressure (IMEP) and the start of combustion angle, θ SOC , as exhaust valve closing is retarded.…”