Evaluation Of The Environmental Benefit Of Using Altervative Fuels On Light-duty Vehicles

Driven by ever-increasing pressure from energy shortage and environmental protection in China,searching for clean and sustainable vehicle alternative fuel has been unavoidable and of priority.In order to better evaluate the expected benefit of the existing alternative options,this thesis raise a method for the evaluation of environemtal benefit of alternative fuel application,the core of the method is a“regulated+unregulated”pollutants,“primary+secondary”contamination-originated idea.By applying this method and comparing to gasoline baseline,this thesis alidates the feasibility of the proposed method,and evaluates the environmental benefits of burning methanol-gasoline,dedicated methanol and natural gas on light-duty vehicles.The result shows that,compared to gasoline,burning methanol-gasoline could reduce CO emission markedly,however,no consistent conclusion can be drawn regarding THC and NOx emissions due to large variations among different vehicle and fuel samples.The use of methanol-gasoline also reduces tailpipe PM and VOCs emissions,but results in increases in PN and carbonyls.Under possible exposure conditions,the concentrations of tailpipe formaldehyde and benzene cannot cause any acute or chronic symptoms.Cancer-related risk attributed to formaldehyde of methanol-gasoline is at the same level with that of gasoline,while cancer risk associate with benzene of methanol-gasoline is lower than that of gasoline.Refilling cars with methanol-gasoline causes much higher evaporative emissions.Burning low-content methanol-gasoline shows lower OFP than gasoline,but high-content methanol-gasoline drives tailpipe pollutants more ozone-inducible.Regardless of energy tax,burning low-content methanol-gasoline could obtain more than 10%cost saving.In general,burning methanol-gasoline emits smaller amount of CO,PM and VOCs emissions than gasoline,however such advantages are far unable to balance its major challenges from intactable THC,NOx,PN and evaporative emissions.Hence,very limited environmental benefits of using methanol-gasoline as a gasoline surrogate can be foreseen.Dedicated methanol-fueled vehicle emits much less CO emission than gasoline counterpart,while the two fuels have similar THC and NOx emissions.Though regulated emissions from field-aged methanol cars surge a lot from the basis of new ones,they could still fulfill the regulatory requirements.Relative to gasoline,burning neat methanol removes about two thirds of PM emissions.Methanol car has higher carbonyls emission than gasoline but emits less VOCs.Engine misfire,which is the largest barrier for methanol car,causes increased CO,THC,unburned methanol and formaldehyde emissions,however the current OBD regulation could hardly cope with this issue.Tailpipe emissions of unburned methanol,formaldehyde and benzene are neither able to result in any acute or chronic symptoms,nor to increase cancer morbidity under assumed exposure conditions.OFP of burning neat methanol is remarkably lower than that of gasoline,but OFP increases with the occurrence of engine misfire.An 8%reduction of CO₂ emission can be attained by switching from gasoline to neat methanol.A decrease of over 40%in fuel cost can be predicted once neat methanol is consumed.Above all,given inmature OBD regulation and unsolved misfire issue,at present,large-scale application of dedicated methanol-fueled vehicles could still increase environmental risk.Burning natural gas instead of gasoline has been shown an effective measure to reduce CO emission,while THC and NOx emissions of the test crew increase significantly.With natural gas fueling,regulated emissions show faster deterioration rates with vehicle ageing than than gasoline,several times of sub-standard THC and NOx emissions are only found in natural gas mode.Compared to gasoline,burning natural gas discharges more PM and carbonyls,but gives less VOCs.When tested with ELPI,PN measured in natural gas mode is also higher.The concentrations of tailpipe formaldehyde and benzene could not lead to any acute or chronic symptoms,cancer-related risks of natural gas and gasoline fueling are at the same level.Part of natural gas cars have serious leakage issue,methane attributed to leakage is far more than tailpipe emission.OFP of burning natual gas is 10%to 20%lower than that of gasoline,while CO₂ emissions from natural gas fueling can be 17%to 19%less.Based on the local price in Beijing,burning natural gas could decrease fuel cost by about 30%during high-oil-price period,however,fuel economy of natual gas becomes even slightly worse than gasoline when international oil price goes down.Generally,the advantages of natural gas on CO and CO₂ emissions could merely leverage its environmental risks come from extra PM and fuel leakage.It should be more conservative to increase the application of natural gas in light-duty vehicle sector.