scholarly journals Cycle-by-cycle variations in autonomous and spark assisted homogeneous charge compression ignition combustion of stoichiometric air–fuel mixture

2018 ◽  
Vol 10 (3) ◽  
pp. 231-243 ◽  
Author(s):  
Jacek Hunicz
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Fuel Injection ◽  
Fuel Mixture ◽  
Compression Ignition ◽  
Indicated Mean Effective Pressure ◽  
Start Of Injection ◽  
Negative Valve Overlap ◽  
Compression Ignition Combustion ◽  
Valve Overlap ◽  
Homogeneous Charge

This study investigates cycle-by-cycle variations in a gasoline fuelled, homogeneous charge compression ignition (HCCI) engine with internal exhaust gas recirculation. In order to study the effects of exhaust-fuel reactions occurring prior to the main combustion event fuel was injected directly into the cylinder at two selected timings during the negative valve overlap period. The engine was operated as both autonomous HCCI and spark assisted HCCI (SA-HCCI). The primary interest in this work was the operating region where the engine is switched between HCCI and spark ignition modes, thus operation with stoichiometric air–fuel mixture, which is typical for this region, was considered. Cycle-by-cycle variations in both combustion timing and indicated mean effective pressure (IMEP) were investigated. It was found that long-period oscillations of the IMEP occur when fuel injection is started at early stages of the negative valve overlap period, and that these can be suppressed by delaying the start of injection. This behaviour remained even when fuel injection was split into early and late-negative valve overlap injections. Spark assisted operation allowed eliminating late combustion cycles, thus improving thermal efficiency. However, characteristic patterns of IMEP variations were found to be the same for both HCCI and SA-HCCI operations, irrespective of the adopted negative valve overlap fuel injection strategy, as evidenced by using symbol-sequence statistics.

Study of diesel-fuelled homogeneous charge compression ignition combustion by in-cylinder early fuel injection and negative valve overlap

2005 ◽  
Vol 219 (10) ◽  
pp. 1193-1201 ◽  
Author(s):  
L Shi ◽  
K Deng ◽  
Y Cui
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Ignition Time ◽  
Combustion Stability ◽  
Inlet Temperature ◽  
Compression Ignition ◽  
Engine Load ◽  
Hcci Combustion ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Homogeneous Charge

This paper presents a scheme to achieve diesel-fuelled homogeneous charge compression ignition (HCCI) combustion, which is to inject diesel fuel directly into the cylinder at near intake top dead centre and adjust the valve overlap to obtain a higher internal exhaust gas recirculation (EGR) in the cylinder. The effects of the engine load, speed, inlet temperature, external EGR, and internal EGR on HCCI combustion and emission were studied. The combustion stability of HCCI combustion was also studied by statistics analysis. The results show the following: when the engine load or inlet temperature increases, which results in a higher in-cylinder temperature, the start of combustion (SOC) is advanced; the ignition time of HCCI relative to the engine crank angle is retarded when the engine speed increases; inert gases contained in the EGR can slow the chemical reaction rate, which can delay the auto ignition time; for the diesel-fuelled HCCI, increasing the negative valve overlap (NVO) makes the SOC advanced and makes the combustion stability better at low loads and worse at high loads. The emission results show that the nitrogen oxides (NOx) and smoke emissions are very low, and a large NVO can decrease the smoke emission but not benefit the NOx emission at high loads for diesel-fuelled HCCI combustion.

Ion current–based homogeneous charge compression ignition combustion control using direct water injection

2020 ◽  
pp. 146808742092783 ◽  
Author(s):  
Denghao Zhu ◽  
Jun Deng ◽  
Raphael Dewor ◽  
Maximilian Wick ◽  
Jakob Andert ◽  
...  
Keyword(s):  
Heat Release ◽  
Homogeneous Charge Compression Ignition ◽  
Water Injection ◽  
Ion Current ◽  
Compression Ignition ◽  
Effective Pressure ◽  
Indicated Mean Effective Pressure ◽  
Direct Water Injection ◽  
Compression Ignition Combustion ◽  
Homogeneous Charge

Homogeneous charge compression ignition has proven to be both highly efficient and to operate with ultra-low NOx raw emissions. However, homogeneous charge compression ignition combustion is a dynamic process due to strong cycle-to-cycle coupling effects caused mainly by the residual gas. Compared to conventional spark-ignited and diesel engines, the lack of direct mixture composition and ignition control increases the challenge of combustion instabilities, especially at boundary conditions. To stabilize the combustion process, real-time in-cylinder combustion diagnostics and control are often used. In this study, for the first time, ion current detection technology and direct water injection are combined for homogeneous charge compression ignition combustion control. By analyzing the return map of the crank angle at 50% cumulative heat release under unstable conditions, it was identified that a misfire or incomplete combustion is usually followed by knocking-like early combustion with high cylinder pressure gradients. Through the correlation analysis between ion current and combustion, a cycle-to-cycle closed-loop control strategy was developed and implemented on a rapid control prototyping engine control unit. Real-time calculated ion current parameters were used to predict the 50% cumulative heat release position of the next cycle and prevent early combustion by direct water injection. The calculation results and controller performance were validated on a single-cylinder research engine. With the controller activated, the standard deviation of 50% cumulative heat release and dynamic programming to the max could be reduced by 19% and 11%, respectively. The coefficient of variation of indicated mean effective pressure was reduced by 12%. A slight increase in indicated mean effective pressure after activating the controller also shows the potential for efficiency improvement. Moreover, not only early combustion is controlled, but also late combustion is significantly reduced.

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