Potentials of airpath variabilities for HD gas engines

Owing to the lower carbon content in the fuel, gas engines can make an important contribution to meeting the future CO2 emission goals for commercial vehicle fleets. In order to prevent uncontrolled auto-ignition, however, these engines must be operated with later ignition crank angles at high loads, while throttling is also necessary at low loads. Both interventions reduce the efficiency of the engine. In the FVV project “Potentials of Airpath Variabilities for HD Gas Engines”, systematic analyses are being conducted for the first time with the aim of determining the degree to which engine efficiency and emissions levels can be improved by closing the inlet valves early (“Miller control times”). Furthermore, the interactions with exhaust gas recirculation, water injection and a possible increase of the geometric compression ratio are also being investigated. The project builds on findings from previous projects on variable valve timings in commercial diesel engines.

Motivation

The combination of spark-ignition and gas combustion processes with stoichiometric air-fuel ratios and three-way catalytic converters is itself an option to combine low CO2 emissions with very good pollutant emission values. However, prior to the start of the FVV project, there were very few scientific findings as to how far efficiency can be increased through variable valve timings. Furthermore, there are no reliable sources on how this interacts with other technologies that are aimed at reducing emissions. The results of the pre-competitive project will allow future generations of gas engines to quickly make a significant contribution to climate protection in road freight traffic.

Methodology

The project at the Technische Universität Braunschweig is based on measurements performed on a single-cylinder research engine. Although the engine has already been used in multiple previous projects on valve train variabilities, it first had to be converted to the combined spark-ignition and gas combustion process for the current project. Following commissioning, measurements will be taken across the entire engine operation range. Here, not only will the valve closing times be varied, but also the compression ratio via the piston. The influence of exhaust gas recirculation and water injection will also be investigated across multiple tests. Based on the data derived from this, the team of researchers will create different models as a basis for a complete engine simulation, with which the CO2 potential is to be determined.

Result

The project began at the start of 2019 and is scheduled for completion by the end of the year. The test bench was successfully converted. A large quantity of measurement data is already available at the start of 2021, meaning that the construction of the simulation models could begin.

Documentation

Downsizing of HD Commercial Vehicle Engines by Airpath Variabilities | Potential of the airpath variabilities on heavy duty engine to improve the performance and optimise the pollutant and CO2 emissions | Funding No. 1065

Downsizing of HD Commercial Vehicle Engines by Airpath Variabilities II | Potential of the airpath variabilities on heavy duty engine to improve the performance and optimise the pollutant and CO2 emissions | Funding No. 1199

Potentials of Airpath Variabilities for HD Gas Engines | Potentials of airpath variabilities for future commercial vehicle gas engines to increase efficiency and reduce emissions | Funding No. 1346

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