Investigation of Gasoline Partially Premixed Combustion with External Exhaust Gas Recirculation

Abstract

The stringent emission regulations for Internal Combustion Engines (ICEs) spawned a great amount of research in the field of innovative combustion approaches characterized by high efficiency and low emissions. Previous research demonstrate that such promising techniques, named Low-Temperature Combustion (LTC), combine the benefits of Compression Ignition (CI) engines, such as high compression ratio and unthrottled lean mixture, with low engine-out emissions using a properly premixed air-fuel mixture. Due to longer ignition delay and high volatility compared to diesel, gasoline-like fuels show good potential for the generation of a highly premixed charge, which is needed to reach LTC characteristics. In this scenario, gasoline Partially Premixed Combustion (PPC), characterized by the high-pressure direct injection of gasoline, showed good potential for the simultaneous reduction of pollutants and emissions in CI engines. However, previous research on gasoline CI highlight that a key factor for the optimization of both efficiency and pollutants is the proper management of Exhaust Gas Recirculation (EGR). This work presents the experimental investigation performed running a light-duty CI engine, operated with gasoline PPC, and varying the mass of recirculated gases trapped in the combustion chamber. To guarantee the stability of gasoline autoignition in all the tested conditions, a specific experimental layout has been developed to accurately quantify the amount of trapped residual gases due to the internal and external EGR. The obtained results clearly highlight the impact of EGR on the combustion process and emissions, demonstrating that optimization of charge dilution with EGR is fundamental to guarantee the optimal compromise between efficiency and emissions over the whole operating range.

Accelerometer-based SOC estimation methodology for combustion control applied to Gasoline Compression Ignition

“…It is important to highlight that GCI combustion typically works with high EGR rates to limit pollutants [15,18], and its impact on the ignition delay (and consequently on SOC) is remarkable. Previous works made by the authors demonstrated that to make stable and reliable GCI combustion, a very strong first combustion stage (related to the combustion of the pilot injections) is mandatory even using high EGR rates [13,20]. As a result, during the whole experimental activity the EGR system has been turned off mainly because its effects on the first combustion stage is negligible in terms of energy released, and consequently on the signalto-noise ratio.…”

“…As documented in literature [18][19][20][21]27], GCI combustion needs high boost pressure and intake temperature to promote the gasoline autoignition. This aspect becomes crucial especially during cranking, idle or at low loads when the exhaust gas energy is not enough to drive the turbocharger reaching the target value of boost pressure.…”

“…Since the literature on remote sensing techniques using accelerometer sensors demonstrated that to maximize the sensitivity on vibration the sensor must be placed on the engine block (bottom part is preferred) [40,41], the sensor positions highlighted by Figure 8 were chosen following this guideline. Position 2 and 3 on the exhaust side By using the engine calibration obtained by the authors through previous activities on the GCI engine [19,20], to evaluate the accuracy of the accelerometer-based SOC estimation methodology with different sensor positions, two different loads were tested: low load, with IMEP equal to 10 bar; high load, with IMEP equal to 14 bar. Table 3 and Table 4 summarize the engine operating conditions for the low load and high load tests respectively.…”

“…Due to the absence of an external device which starts the combustion, the energy released by the small amount of fuel introduced with pilot injections plays a crucial role on the whole combustion management. As a matter of fact, the rise of in-cylinder pressure and temperature generated by the fuel injected with pilot injections (chemically driven by nature) allows to reduce the ignition delay of the following injection which burns in stratified conditions, thus generating a smoother combustion shape [18][19][20]. However, since the first fuel jets burns as an HCCI combustion, a proper injection strategy management is mandatory to guarantee safety GCI combustion which provides the delivered torque with a defined center of combustion (CA50).…”

Modeling the impact of the fuel injection strategy on the combustion and performance characteristics of a heavy-duty GCI engine

“…1 Conventional CI engines operating on diesel fuel have high thermal efficiency, but they suffer from high soot emissions and NOx due to heterogeneous fuel air mixtures and high combustion temperatures. 2 In order to achieve the best of both combustion modes, several advanced concepts like homogeneous charge compression ignition (HCCI) 3,4 reactivity controlled compression ignition (RCCI) [5][6][7] ,gasoline compression ignition (GCI), 8,9 partially premixed combustion (PPC), 10,11 etc. have been proposed in the literature.…”