Drive Cycle Analysis of Load Control Strategies for Methanol Fuelled ICE Vehicle 2012-01-1606
The use of methanol as spark-ignition engine fuel can help to increase energy security and offers the prospect of carbon neutral transport. Methanol's properties enable considerable improvements in engine performance, efficiency and CO2 emissions compared to gasoline operation. SAE paper 2012-01-1283 showed that both flex-fuel and dedicated methanol engines can benefit from an operating strategy employing exhaust gas recirculation (EGR) to control the load while leaving the throttle wide open (WOT). Compared to throttled stoichiometric operation, this reduces pumping work, cooling losses, dissociation and engine-out NOx.
The current paper presents follow-up work to determine to what extent these advantages still stand over an entire drive cycle. The average vehicle efficiency, overall CO2 and NOx emissions from a flexible fuel vehicle completing a drive cycle on gasoline and methanol were evaluated. Next, the throttled and WOT EGR strategy were compared in terms of drive cycle efficiency and emissions for both a flex-fuel and a dedicated methanol vehicle. The analysis was done using Lotus Vehicle Simulation and was based on steady state experimental results obtained from a single cylinder research engine and a turbocharged four cylinder diesel that was converted for SI operation on methanol.
Our results indicate that over an entire drive cycle using methanol in a flex-fuel vehicle enables a relative efficiency benefit compared to gasoline of more than 3.5%pt while reducing the CO2 emissions and engine-out NOx apprx. 20% and 90% respectively. The benefits of the WOT EGR strategy are most pronounced for the turbocharged four-cylinder engine, which thanks to its high compression ratio and elevated level of in-cylinder turbulence allows throttleless load control down to 3 bar BMEP. This results in drive cycle efficiencies and CO2 emissions comparable to the baseline diesel engine.