Effects of EGR, Variable Valve Timing, High Turbulence and Water Injection on Efficiency and Emissions of a HD Stoichiometric Natural Gas Engine

The EU recently decided to reduce CO₂ emissions of commercial vehicle fleets by 30% until 2030. One possible way to achieve this target is to convert commercial vehicle diesel engines into stoichiometric natural gas engines. Based on this, a commercial vehicle single cylinder diesel engine with variable valve actuation and high-pressure EGR is converted into natural gas operation to increase efficiency and thus reduce CO₂. Additionally, a water injection system is integrated. All three technologies are investigated on their own and in combination. To reduce longer combustion durations caused by Miller valve timing and charge dilution, a piston bowl with extra high turbulence generation is designed. Additionally, a swirl variation is carried out. The results show, that high swirl motion and high turbulence can lead to a disadvantage in efficiency despite faster combustion durations due to higher wall heat losses. However, by using suitable combinations, it is possible to minimize throttle losses in low load operation and achieve optimum combustion locations (8°CA aFTDC) at full load operation with conventional compression ratios (ε=12). This allows for an increase in geometric compression ratio and thus in efficiency. Efficiency improvements of over 2 %-points have been achieved at full load with common natural gas (MN ~81.5). This helps to fulfil future CO₂/NO_x legislations for HD commercial vehicle engines.