Combined Technologies for Efficiency Improvement on a 1.0 L Turbocharged GDI Engine 2019-01-0233

The CO₂ reduction request for automotive industry promotes the efforts on the engine thermal efficiency improvement. The goal of this research is to improve the thermal efficiency on an extremely downsized 3-cylinder 1.0 L turbocharged gasoline direct injection engine. Effects of compression ratio, exhaust gas recirculation (EGR), valve timing and viscosity of oil on fuel economy were studied. The results show that increasing compression ratio, from 9.6 to 12, can improve fuel economy at relative low load (below 12 bar BMEP), but has a negative effect at high load due to increased knock intensity. EGR can significantly reduce the pumping loss at low load, optimize combustion phase and reduce exhaust gas temperature. Therefore, the fuel consumption is reduced at all test points. The average brake thermal efficiency (BTE) benefit percentage is 3.47% with 9.6 compression ratio and 5.33 % with 12 compression ratio. However, at higher load (over 18 bar BMEP), EGR needs to be reduced to reach the target load, which would affect its benefit to efficiency.

Combined high compression ratio with EGR, the maximum BTE increased from 36.55% to 38.95% at 2500 rpm 14 bar BMEP, in which compression ratio and EGR contribute an absolute increase of BTE by 0.36% and 2.04% separately. Based on that, valve timing was optimized, and lower viscosity oil was used. The maximum BTE was further enhanced to 39.53%, in which optimization of valve timing and lower viscosity oil contribute an absolute increase of BTE by 0.24% and 0.34% separately.

Besides, engine performance at full load was investigated. The results show that there is power loss at full load after increasing compression ratio. EGR is not applicable to recover the torque with high compression ratio, in contrast, it would increase combustion instability and decrease the torque. Fuel enrichment and reducing coolant temperature are two effective ways to recover the torque but sacrificing engine efficiency.