Dual fuel low temperature combustion (LTC) strategies are attractive for future internal combustion engines due to their promise of very low engine-out emissions of oxides of nitrogen (NO x) and particulate matter. In the present work, experimental results for diesel-ignited methane dual fuel LTC on a compression ignition single cylinder research engine (SCRE) are presented. Methane was fumigated into the intake manifold and diesel injection was used to initiate combustion. The engine was operated at a constant speed of 1500 rev/min, and diesel injection pressure was fixed at 500 bar. The start of injection (SOI) of diesel fuel was varied from 260º to 360º (i.e., TDC) to quantify its impact on engine performance and engine-out, indicated-specific emissions of NO x (ISNO x), carbon monoxide (ISCO), and unburned hydrocarbons (ISHC), and smoke emissions. The SOI sweeps were performed at different net indicated mean effective pressures (IMEPs) of 4.1 and 12.1 bar. Intake manifold pressure and methane percent energy substitution (PES) were fixed at 1.5 bar and 80%, respectively, for 4.1 bar IMEP and at 1.8 bar and 95%, respectively, for 12.1 bar IMEP. For all loads, when SOI was advanced, the longer ignition delays caused the separation between the fuel injection and the combustion events to increase. This was accompanied by a change in the shape of the AHRR curve from a distinct two-stage profile to a smooth, single-stage (almost Gaussian) profile.

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P erform ance and Em issions C haracteristics of D ie s e l-Ig n ite d G asoline D ual Fuel Com bustion in a S in g le -C y lin d e r R esearch EngineDiesel-ignited gasoline dual fu el combustion experiments were performed in a singlecylinder research engine (SCRE), outfitted with a common-rail diesel injection system and a stand-alone engine controller. Gasoline was injected in the intake port using a port-fuel injector. The engine was operated at a constant speed o f 1500 revlmin, a con stant load o f 5.2 bar indicated mean effective pressure (IMEP), and a constant gasoline energy substitution o f 80%. Parameters such as diesel injection timing (SOI), diesel injection pressure, and boost pressure were varied to quantify their impact on engine per formance and engine-out indicated specific nitrogen oxide emissions (ISNOx), indicated specific hydrocarbon emissions (ISHC), indicated specific carbon monoxide emissions (ISCO), and smoke emissions. Advancing SOI from 30 degrees before top dead center (DBTDC) to 60 DBTDC reduced ISNOx from 14 glkW h to less than 0.1 g/kW h; further advancement o f SOI did not yield significant ISNOx reduction. A fundamental change was observed from heterogeneous combustion at 30 DBTDC to ''premixed enough" com bustion at 50-80 DBTDC and finally to well-mixed diesel-assisted gasoline homogeneous charge compression ignition (HCCI)-like combustion at 170 DBTDC. Smoke emissions were less than 0.1 filter smoke number (FSN) at all SOls, while ISHC and ISCO were in the range o f 8-20 glkW h, with the earliest SOIs yielding very high values. Indicated fuel conversion efficiencies were ~ 40-42.5%. An injection pressure sweep from 200 to 1300 bar at 50 DBTDC SOI and 1.5 bar intake boost showed that very low injection pressures lead to more heterogeneous combustion and higher ISNOx and ISCO emissions, while smoke and ISHC emissions remained unaffected. A boost pressure sweep from 1.1 to 1.8 bar at 50 DBTDC SOI and 500 bar rail pressure showed very rapid combustion fo r the lowest boost conditions, leading to high pressure rise rates, higher ISNOx emissions, and lower ISCO emissions, while smoke and ISHC emissions remained unaffected by boost pressure variations.

D ep a rtm e n t o f M e cha n ical E n g in e erin g, C enter fo r A d va nce d V e h ic u la r S ystem s, M is s is s ip p i State U nive rsity, M is s is s ip p i State, M S 3 9 7 6 2 e -m a il: krishn a n @ m e .m sstate .e du D iesel-Ignited Propane Dual Fuel Low Tem perature Combustion in a Heavy-Duty Diesel EngineThis paper presents an experimental analysis of diesel-ignited propane dual fuel low tem perature combustion (LTC) based on performance, emissions, and in-cylinder combustion data from a modern, heavy-duty diesel engine. The engine used for these experiments was a 12.9-liter, six-cylinder, direct injection heavy-duty diesel engine with electronic unit diesel injection pumps, a variable geometry turbocharger, and cooled exhaust gas recirculation (EGR). The experiments were performed with gaseous propane (the primary fuel) fumigated upstream of the turbocharger and diesel (the pilot fuel) injected directly into the cylinders. Results are presented for a range of diesel injection timings (SOIs) from 10 deg BTDC to 50 deg BTDC at a brake mean effective pressure (BMEP) of 5 bar and a constant engine speed of 1500 rpm. The effects of SOI, percent energy substitution (PES) o f propane (i.e., replacement of diesel fuel energy with propane), intake boost pressure, and cooled EGR on the dual fuel LTC process were investigated. The approach was to determine the effects of SOI while maximizing the PES of propane. Dual fuel LTC was achieved with very early SOIs (e.g., 50 deg BTDC) coupled with high propane PES (>84%), which yielded near-zero NOx (<0.02 glkW h) and very low smoke emissions (<0.1 FSN). Increasing the propane PES beyond 84% at the SOI of 50 deg BTDC yielded a high COV oflMEP due to retarded combustion phasing (CA50). Intake boost pressures were increased and EGR rates were decreased to minimize the COV, allowing higher propane PES (~93%); however, lower fuel conversion efficiencies (FCE) and higher HC and CO emissions were observed.

This paper presents an experimental analysis of diesel-ignited propane dual fuel low temperature combustion (LTC) based on performance, emissions, and in-cylinder combustion data from a modern, heavy-duty diesel engine. The engine used for these experiments was a 12.9-liter, six-cylinder, direct injection heavy-duty diesel engine with electronic unit diesel injection pumps, a variable geometry turbocharger, and cooled exhaust gas recirculation (EGR). The experiments were performed with gaseous propane (the primary fuel) fumigated upstream of the turbocharger and diesel (the pilot fuel) injected directly into the cylinders. Results are presented for a range of diesel injection timings (SOIs) from 10° BTDC to 50° BTDC at a brake mean effective pressure (BMEP) of 5 bar and a constant engine speed of 1500 RPM. The effects of SOI, percent energy substitution (PES) of propane (i.e., replacement of diesel fuel energy with propane), intake boost pressure, and cooled EGR on the dual fuel LTC process were investigated. The approach was to determine the effects of SOI while maximizing the PES of propane. Dual fuel LTC was achieved with very early SOIs (e.g., 50° BTDC) coupled with high propane PES (> 84%), which yielded near-zero NOx (< 0.02 g/kW-hr) and very low smoke emissions (< 0.1 FSN). Increasing the propane PES beyond 84% at the SOI of 50° BTDC yielded a high COV of IMEP due to retarded combustion phasing (CA50). Intake boost pressures were increased and EGR rates were decreased to minimize the COV, allowing higher propane PES (∼ 93%); however, lower fuel conversion efficiencies (FCE) and higher HC and CO emissions were observed.