Potential of alcohol fuels in active and passive pre-chamber applications in a passenger car spark-ignition engine

Abstract

Both the shift from fossil to alternative fuels and the implementation of a pre-chamber combustion system allow for an increase in the efficiency of an internal combustion engine through optimizing its combustion process, while simultaneously reducing the engine-out emissions. The combination of alcohol-based fuels and pre-chamber combustion concepts has not been investigated on spark-ignition engines with high compression ratios in a passenger car size. This study presents investigations to show the potential in maximum achievable lean limit and net indicated efficiency. In particular, we present investigations of two alternative alcohol fuels on a direct-injection spark-ignition single-cylinder research engine for passenger car applications with a compression ratio of 16.4. The engine was operated with both an active and a passive pre-chamber, and the experimental results were compared to those of conventional spark-ignition operation. Direct injection was used for both the main combustion chamber and the pre-chamber. Methanol and ethanol were used as fuels for the main combustion chamber, whereas exclusively ethanol was used for the pre-chamber fueling. The performance of the alcohol fuels in all combustion configurations was evaluated in both part-load and high-load conditions. In particular, investigations of the combustion behavior over a variation of the excess air ratio at indicated mean effective pressures of 6 and 15 bar were performed. It can be concluded that with the use of methanol as fuel for the main combustion chamber, both higher excess air ratios and higher indicated efficiencies were achieved compared to the use of ethanol as the main combustion chamber fuel. In particular, a maximum net indicated efficiency of 48% at an excess air ratio of 2.0 was achieved with methanol. Moreover, active pre-chamber operation extended the lean limit to an excess air ratio of 2.3 compared to the maximum lean limit of 1.7 in passive pre-chamber operation.

Renewable Methanol as a Fuel for Heavy-Duty Engines: A Review of Technologies Enabling Single-Fuel Solutions

“…This extension is attributed to the fuel enrichment of the PC, resulting in stable and strong jets capable of successfully igniting the much leaner MC mixture. Consequently, this leads to significantly lower NO x emissions, as these emissions are strongly correlated with global λ. Near-zero NO x emissions of 0.07 g/kWh were measured at λ = 2.2 utilizing methanol, compared with NO x emissions exceeding 10 g/kWh at λ = 1 [117]. However, as λ increases, so do HC emissions, although, with PC combustion, the increase in HC emissions is less pronounced than in traditional SI operations due to the faster combustion [117].…”

“…Consequently, this leads to significantly lower NO x emissions, as these emissions are strongly correlated with global λ. Near-zero NO x emissions of 0.07 g/kWh were measured at λ = 2.2 utilizing methanol, compared with NO x emissions exceeding 10 g/kWh at λ = 1 [117]. However, as λ increases, so do HC emissions, although, with PC combustion, the increase in HC emissions is less pronounced than in traditional SI operations due to the faster combustion [117]. Nonetheless, there remains a trade-off between NO x and HC emissions.…”

“…Nonetheless, it is essential to note that each In recent years, pre-chamber technology has gained interest as a means to facilitate the use of renewable fuels in ICEs, next to improving combustion with classic fossil fuels. Research has explored the feasibility of employing pre-chambers with a variety of renewable fuels [110,[117][118][119][120][121]. Many of these possess high octane numbers, rendering them challenging to ignite in CI engines.…”

“…A comparison between methanol and ethanol was performed by Burkardt et al [117]. The experiments were conducted using a similar light-duty engine, specifically a 0.5 L single-cylinder DI research engine with a bore of 75 mm, a stroke of 113 mm, and a CR of 16.4 was used.…”

“…In their research on PCs in light-duty engines, Burkardt et al [117] and Harrington et al [126] also investigated active layouts. Both concluded that active PCs have a significantly extended lean limit compared to their passive counterparts.…”