Studies using a bi-fuelled (autogas/gasoline) Renault Laguna vehicle meeting °the 1996 European exhaust emission legislation has demonstrated that over the European test cycle at 25°C the LPG operated vehicle provides substantial benefits of reduced emissions compared to unleaded reference gasoline. At lower test temperatures (i.e. 5°C) even larger reduction in emissions have been observed. Lower CO (up to 95% at -5°C and 65% at 25°C), HC (90% at -5°C and 40% at 25°C) emissions and lower ozone HC reactivity have been observed and could all offer significant environmental air-quality benefits for LPG.
Various autogas mixtures have been tested including 70/30, 30/70 and 49/30/21 (% mass propane / butane / propene). Results show that NOx emissions for this vehicle appear dependent on autogas composition. The two gas mixtures containing only 30% butane gave about 50% more NOx at +25°C than the 70% butane autogas mixture. At -5°C the gas containing 21% propene gives higher NOx emissions (by ∼30%) than the two gases without unsaturated components. These trends were similar over the ECE 1+2, 3+4 and EUDC phases of the European drive cycle. At -5°C all the gas mixtures show a NOx reduction compared to the reference gasoline. Benzene and 1,3 butadiene emissions (2 of the US EPA air-toxics) were also very low (<lmg/km) when fuelled on autogas. Volumetric fuel consumption for all gas mixtures was higher than gasoline, although by mass all LPG blends showed a marginal improvement in economy. Limited tests have been carried out over the proposed European drive cycle (11 seconds idle, with emission sampling from start of test). Results show an increase in CO and HC emissions at 25°C, when operating, on 70/30 propane/butane mixture over the proposed cycle compared to the current drive cycle.
Earlier programmes of work using a Renault Clio and a Renault Express vehicle, both fitted with the same engine type (1.4 ltr) and three-way catalysts, but with different LPG fuelling systems (Vialle evaporative without self-learning capability and NECAM multi-point gas injection systems) showed similar emission benefits. Over the European test cycle at 25°C both LPG fuelling systems showed that HC, CO and NOx emissions were reduced by up to 50%. At lower test temperatures (i.e. -5°C), autogas mixtures showed a larger reduction in emissions compared to gasoline (up to 70%). In these programmes, fuel consumption with LPG was slightly higher by volume (11%) but lower by mass (22%) compared to gasoline although consumption, by volume, was improved with increasing butane content. Variation in the composition of the autogas mixture from 99% propane to 30/70 propane/butane mixtures (% mass) had only a small effect on HC and CO emissions, particularly for the vehicles fitted with fully adaptive AFR feed back engine management control, but significantly decreased NOx emissions on these vehicles and at all test conditions.