Efficient light-duty engine using turbulent jet ignition of lean methane mixtures

Abstract

Diesel engines use diffusion-controlled combustion of a high-reactivity fuel and offer high efficiencies because they combine lean combustion with a high compression ratio. For low-reactivity fuels such as gasoline or natural gas, premixed combustion is used, which leads to lower efficiency levels as usually stoichiometric combustion is combined with lower compression ratios. Trying to apply diesel-like process parameters to low-reactivity fuels inevitably leads to problems with classical spark ignition systems as they are not able to establish robust flame propagation for such hard-to-ignite conditions. One possibility to enable fast combustion for diluted mixtures at high pressure levels is to establish ignition in a prechamber and ignite the charge of the main combustion chamber using the turbulent jets exiting the prechamber. In this study, the experimental results of a prechamber-equipped four-cylinder natural gas engine with 2 L displacement are discussed in detail. In the majority of the engine map, auxiliary fueling is used in the prechamber and a global air–fuel equivalence ratio λ is set to 1.7. At full load, a λ of 1.5 is applied without auxiliary prechamber fueling. The experiments show that such a setup is able to achieve brake efficiency levels of above 45% while maintaining peak brake mean effective pressure levels above 20 bar. At high load conditions, cylinder pressure levels at ignition timing achieve more than 80 bar and cylinder peak pressures of around 180 bars occur. The technology proved to enable robust and very fast combustion at comparably low NOx levels. A remaining challenge for the on-road use of such a technology is the reduction of the methane emissions at lean conditions.

Jet ignition prediction in a zero-dimensional pre-chamber engine model

“…Attard et al 7,8 have demonstrated the capability of the PCI concept, increasing the air dilution limit above = 2.0 while maintaining very high levels of engine e ciency. This has been confirmed in more recent studies 9,10 .…”

Effect of the Intake Valve Lift and Closing Angle on Part Load Efficiency of a Spark Ignition Engine

“…The center of combustion, estimated online with the Rassweiler and Withrow method [10], was set to 368 • CA by closed-loop-control of the ignition angle. This value was chosen for all the experiments as it gives the highest efficiency (or maximum brake torque, respectively) and it ensured stable operation [11]. Figure 1 (right) provides a picture of the test-bench setup (engine and entire control unit) and Table 1 lists the main characteristics of the experimental setup.…”

Increased Internal Combustion Engine Efficiency with Optimized Valve Timings in Extended Stroke Operation

“…Thus, the thermal efficiency is increased due to the extended expansion stroke relative to the compression stroke [17]. If a suitable exhaust aftertreatment system is used, lean combustion concepts with pre-chamber or pilot ignition lead to a significant increase of the thermal efficiency [18,19] and efficiency levels of above 45% are achievable for passenger car size engines [20]. Cooled exhaust gas recirculation in combination with variable compression ratios allows for improvement of the thermal efficiency, while the formation of emissions such as nitrogen-oxides (NO x ) and hydrocarbons (HC) are decreased [21].…”