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The application of short burn durations at lean engine operation has the potential to increase the efficiency of spark-ignition engines. To achieve short burn durations, spark-assisted compression ignition (SACI) as well as active pre-chamber (PC) combustion systems are suitable technologies. Since a combination of these two combustion concepts has the potential to achieve shorter burn durations than the application of only one of these concepts, the concept of jet-induced compression ignition (JICI) was investigated in this study. With the JICI, the fuel is ignited in the PC, and the combustion products igniting the charge in the main combustion chamber (MC) triggered the autoignition of the MC charge. A conventional gasoline fuel (RON 95 E10) and a Porsche synthetic fuel (POSYN) were investigated to assess the fuel influence on the JICI. Variations of the relative air/fuel ratio in the exhaust gas (λex) were performed to evaluate both the occurrence of the JICI and the dilution capability. To assess the sensitivity of the JICI, variations of the engine speed and the engine load were performed. When using RON 95 E10, a shift from a conventional PC combustion to the JICI was observed between λex = 2.3 and λex = 2.5. The variations of the engine speed and the engine load revealed an increased JICI intensity when the engine speed decreased and when the engine load increased. When using POSYN, no JICI was observed. The occurrence of the JICI was correlated to the knock resistances of the fuels, i.e., the lower knock resistance of RON 95 E10 yielded the JICI, whereas the higher one of POSYN did not. At λex = 2.8, applying POSYN resulted in an increase of the burn duration of 5.5°CA, which was a relative increase of 41%, compared to the use of RON 95 E10 due to the absence of the JICI in case of POSYN. However, the application of POSYN resulted in the highest net indicated efficiency (ηi,net). In particular, the application of RON 95 E10 yielded a maximum of ηi,net = 41.5% at λex = 2.6, whereas using POSYN resulted in a maximum of ηi,net = 42.6% at λex = 2.2 due to the higher knock resistance of POSYN.

Prospective combustion engine applications require the highest possible energy conversion efficiencies for environmental and economic sustainability. For conventional Spark-Ignition (SI) engines, the quasi-hemispherical flame propagation combustion method can only be significantly optimized in combination with high excess air dilution or increased combustion speed. However, with increasing excess air dilution, this is difficult due to decreasing flame speeds and flammability limits. Pre-Chamber (PC) initiated jet ignition combustion systems significantly shift the flammability and flame stability limits towards higher dilution areas due to high levels of introduced turbulence and a significantly increased flame area in early combustion stages, leading to considerably increased combustion speeds and high efficiencies. By now, vehicle implementations of PC-initiated combustion systems remain niche applications, especially in combination with lean mixtures. This is also due to challenges regarding cold-start, combustion stability at low loads, and emissions. Nevertheless, PC ignition systems allow overall engine efficiencies >45%. Therefore, a market launch of an engine using globally lean mixtures ignited by a PC system is desirable. This requires a fast-running and predictive physical model to conduct robust design studies and complement existing testing methodologies (3D-CFD, experimental). This paper addresses the development of a quasi-dimensional burn rate model for PC ignition combustion systems. The presented modeling approach combines the well-established two-zone entrainment model (main-chamber) with a semi-empirical PC model that aims to detect the PC influence on the main-chamber combustion. Dedicated models predict the impact of the jet-induced turbulence and the increased flame area. The models are integrated into the so-called cylinder module developed at IFS (Institute of Automotive Engineering Stuttgart). For the model validation, measurement data of a single-cylinder research engine using different fuels (E1001, RON95E102), loads (IMEP = 6 − 15 bar), excess air dilutions (λ = 1 − 2) and compression ratios (16.41, 12.62) are used, showing a satisfactory prediction of the burn rate and pressure curve.

Regulations around the globe are driving the adoption of alternative fuels and vehicles through the implementation of stricter standards aimed at reducing carbon footprint and criteria emissions such as nitrogen oxides (NOx), particulate matter (PM), and total hydrocarbon (THC) emissions. Low emission zones have been implemented across Europe which restrict access by some vehicles with the aim of improving the air quality. The Paris Agreement on climate change declared governments’ intentions to reduce greenhouse gas (GHG) emissions as outlined in each country’s nationally determined contribution. Providing affordable energy to support prosperity while reducing environmental impacts, including the risks of climate change, is the dual challenge for the energy and transport industries. Development and deployment of low-emission liquid fuels and complementary engine hardware optimization could provide options to meet air quality as well as proposed, ambitious greenhouse gas (GHG) reduction targets. To take advantage of these potential benefits, these fuels must be compatible with the existing fleet and comply with current fuel standards. This work represents a joint effort by Porsche and ExxonMobil Research & Engineering Company. The goal of this work is to evaluate the potential of low-emission fuels to improve tailpipe emissions from in-use and new vehicle fleets. In this study, a number of fuels with various qualities and low-emissions potential were tested for resulting criteria emissions (NOx, PM, THC). A research Porsche single cylinder engine, including advanced engine combustion design elements, was used for combustion and emissions analysis. The tests were done under stationary and dynamic load as well as under different temperature conditions. Significant reductions to criteria emissions were obtained with the new fuel formulations, when compared to an existing European market fuel. Reductions of more than 90% in particulate emissions, 10 to 20% in NOx emissions, and up to 30% in THC emissions were achieved. Additionally, vehicle test results on both, a 1996 993 and a 2016 991.2 Porsche Carrera, with some selected fuels are presented and compared. Emission reduction potential with the 993 (23 years old vehicle) were similar to the 991.2 by using the low emission formulations showing the potential of the fuels in legacy vehicles, not equipped with gasoline particulate filters (GPF), to comply with current emission regulations. Furthermore, these fuels can be formulated to be compliant with existing European fuel regulations.