Paper title : Natural Gas fueled spark- ignition(SI) and Compression-ignition(CI) engine performance and emissions Review done By : Chandra Shekhar Vishwanadha 4/28/2015

Introduction This paper talks about Natural gas as an alternate fuel for conventional Engines Effect on Performance and Emissions by using NG in SI Engines Effect on Performance and Emissions by using NG in CI Engines NG Direct Injection in SI and CI Engines

Effect on Performance by using NG in SI Engines Observation Increased Thermal Efficiency Power generated is less than Gasoline Engines Lower Energy density of NG results in lower volumetric efficiency Lower flame speed Low EGR operability

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Effect on Emissions by using NG in SI Engines Observation Overall decreased emissions[ CO and NMHC] compared to gasoline engines CO 2 emissions decreased NO x emissions increased by 170% MHC emissions increased by 160% Reasons Lower equivalence ratio operation leads to less CO and NMHC emissions As CO 2 emitted per unit mass of NG is 6.7% less Higher combustion temperature and cyl. Pressures as a result of high CR and lean operation EGR and inert gas dilution can be used to mitigate No x also resulting in slow combustion. Hydrogen gas added with EGR helps reducing un-burnt HC and CO MHC is due to flame quenching and adsorption in lube oil and inside crevice volume

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Effect on Performance by using NG in CI Engines Observation Power generated is less than conventional diesel engines NG have less ignition controllability in both port injection and DI Dual Fuel (Pilot fuel and NG) Low (ηvol) High knocking in high loads Discrepancy in power generated increases in high load operations Reasons (F/A)st is 19% less than Diesel Auto-ignition results in multiple flame sources hence less controllability Helps in NO x and smoke mitigation Apparatus design as NG flows via steel tube which takes space and low ṁ in high engine speeds Combustion is faster for NG as compared to Diesel and hence Pressure rise rate is high High speeds the NG+air charge sucked by the engine is less due to design considerations

Effect on Performance by using NG in CI Engines (ctd.) Observation (ηth) discrepancy decreases with increasing load and is similar to Convention diesel engine At high loads Uncooled EGR reduces knocking High EGR with Hydrogen substitution increases Peak HRR and decreases COV in IMEP Reasons Depends on the induction system of fuel Reduces the available oxygen and increases the ignition delay Hydrogen substitution increases the flame speed and imparts stability in combustion despite of high EGR and hence higher ignition delay.

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Effect on Emissions by using NG in CI Engines Observation Overall CO2 decreased emissions compared to diesel engines NO x emissions decreased Smoke, soot and PM decreased Part load HC emissions increased CO emissions increased in part loads and decreased in higher loads Reasons As CO 2 emitted per unit mass of NG is 12.5% less Lower combustion temperature as a result of slower flame and hence resulting in drop in the peak pressure Higher H/C ratio result in better mixing hence less sooting tendencies Hydrogen gas added with EGR helps reducing un-burnt HC and CO Unburnt MHC is due to improper combustion as flame initiated by pilot fuel isnt able to sustain in NG Improper combustion at part loads lead to more production of CO

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DI in Spark Ignition engines Volumetric efficiency increases Increased turbulent mixing and flame speed Increased lean mixture operability High NOx as temp inside Cyl is high Increased CR DI in Compression Ignition Thermal efficiency is consistent NOx and PM decreases

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