Effects of exhaust gas recirculation in homogeneous charge compression ignition engines

Abstract

Ignition control is an important issue in homogeneous charge compression ignition (HCCI) engines, which have the advantages of low NOx emission and high thermal efficiency. In this study, the effect of the exhaust gas recirculation (EGR) on the ignition control of HCCI engines is discussed using an engine cycle simulation in which a homogeneous mixture is assumed. Auto-ignition of 65 per cent iso-octane + 25 per cent toluene + 10 per cent n-heptane, which is used as a fuel to evaluate the characteristics of a gasoline-like fuel, is represented by a detailed reaction model. The dilution by EGR delays the ignition timing when the charged gas temperature is not changed by EGR. The temperature rise of the charged gas promotes auto-ignition. Based on these characteristics, it was suggested that the ignition timing could be controlled by EGR with temperature control, when the amount of fuel supply is constant. This control method can also be applied to control of the air-fuel ratio (A/F) in the cylinder while maintaining the optimum ignition timing. In spite of the difference in the A/F and the EGR ratios, no significant difference was found in the pressure rise rate at combustion and the NOx emission when the ignition timing was the same.

Dilution Effects on the Controlled Auto-Ignition (CAI) Combustion of Hydrocarbon and Alcohol Fuels

“…al. [16]. They used a combination of a piston mounted in the cylinder head (to vary the combustion chamber geometry) and varying quantities of external EGR as two tools for timing control.…”

“…Although the use of burned gas residuals has so far proven to be the most practicable for achieving CAI, there has been a limited amount of detailed work investigating the effects of exhaust gas dilution on CAI or HCCI combustion [3,4,8,11,16]. Thring [4] investigate the effects of A/F ratio, EGR rate, fuel type, and compression ratio on the attainable homogenous CAI combustion region and engine-out emissions.…”

“…Honda ARC 250), it is a main objective of current research to transfer the technology to 4-Stroke engines to eliminate problems associated with the gas exchange process of 2-Stroke engines that result in higher emissions. Many studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] have shown that the known strategies for achieving this type of combustion in any engine can lead to severe restrictions on the load and/or speed range attainable, for a variety of reasons. Development of practical systems [15,18,20] appears to be focussed on hybridisation of CAI technology with those already existing (SI, CI, Electric) to provide a complete power plant retaining all of the benefits of CAI combustion (low emissions, high efficiency) without the drawbacks (limited speed and load range).…”

On the combination of high-pressure and low-pressure exhaust gas recirculation loops for improved fuel economy and reduced emissions in high-speed direct-injection engines

“…On the other hand, despite the development in NO x after-treatment for Diesel engines, EGR remains a cost-effective solution to fulfil current and future NO x emissions regulations. Also, despite they are not widespread, during the last decade several combustion modes such as HCCI (Homogeneous Charge Compression Ignition) [3], PCCI (Premixed Controlled Compression Ignition) [4] or MKI (Moduled Kinetics) [5] have been studied in order to strongly reduce particles and NOx emissions without BSFC damage and it should be noted that the EGR is a key technique to control such combustion processes [6,7].…”

Opposing effects of recirculated gases during cranking on cold start of diesel engines

“…Several factors , such as ambient temperature and pressure [1,[5][6][7][8][9][10]11], the combustion chamber design [11,12,13], the fuel properties [14,15,16], the injection process [1,6,7,17], cranking speed [6,7,11,17], residuals composition, equivalence ratio, surface temperature and the inlet charge temperature [ 14,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], affect the combustion process and engine-out emissions.…”