Injection Strategy and EGR Optimization on a Viscosity-Improved Vegetable Oil Blend Suitable for Modern Compression Ignition Engines 2020-01-2141

To comply with the ambitious CO₂ targets of the European Union, greenhouse gas emissions from the transport sector should be eliminated by 2050. Incremental powertrain improvement and electrification are only a part of the solution and need to be supplemented by carbon-neutral fuels. Due to the high technology readiness level, biofuels offer a short-term decarbonization measure. The high process energy demand for transesterification or hydrotreating however, hinders the well-to-wheel CO₂ reduction potential of current market biodiesels. An often-raised, economically and energetically feasible alternative is to use unprocessed oils with viscosity and cold-properties improvers instead. The present work investigates the suitability of one such biofuel (Plantanol^TM) for advanced common rail engines operating in a partially premixed compression ignition mode. Preliminary investigations are carried out on a Euro VIb light-duty car engine. The main focus is on the influence of the fuel blend on the soot/NO_X emission trade-off without changing the engine control maps. Single-cylinder engine tests are then focused on the optimization potential of injection parameters and external EGR to reach optimum performance-emissions trade-off on the new fuel. The results highlight that at the factory map setting, without EGR, biofuel offers slightly reduced thermal efficiency with respect to diesel, as a joint effect of retarded combustion and elevated THC and CO emissions. NO_X emissions are reduced by 20% at both non-EGR and to 25% EGR operation. With injection parameters optimization, the combustion phasing can be adjusted to diesel-like values while keeping the NO_X reduction benefits. The tested bio-oil blend is however sensitive to EGR, where increasing the recirculation rate retards the combustion while the soot emissions increase almost five-fold over the non-EGR baseline.