A. C. Polk

Detailed characterization of diesel-ignited propane and methane dual-fuel combustion in a turbocharged direct-injection diesel engine

This paper presents an experimental analysis of dual-fuel combustion based on the performance, emissions, and in-cylinder combustion measurements with gaseous propane or gaseous methane as the primary fuel and diesel as the pilot fuel. Two different sets of experiments were performed on a 1.9 litre four-cylinder engine at a constant engine speed of 1800 r/min: first, constant-pilot-quantity experiments, allowing the primary fuel concentration and the brake mean effective pressure to vary; second, constant-brake-mean-effective-pressure experiments, allowing the percentage energy substitution of the primary fuel and the pilot quantity to vary. In the constant-pilot-quantity experiments, the apparent heat release rate profiles showed the influence of the preignition chemistry and gaseous fuel burn rates on the dual-fuel combustion phasing and duration, the fuel conversion efficiency, and the engine-out emissions. With a fixed pilot quantity, the nitrogen oxide emissions were either reduced or unaffected while the smoke levels were increased or unaffected with increasing primary fuel concentration. The carbon monoxide and total unburned hydrocarbon emissions decreased and the fuel conversion efficiency increased as the pilot quantity or the primary fuel concentration was increased. Overall, diesel–propane combustion yielded higher carbon monoxide emissions, lower total unburned hydrocarbon emissions, and slightly higher fuel conversion efficiencies than diesel–methane combustion did. In the constant-brake-mean-effective-pressure experiments, at a brake mean effective pressure of 2.5 bar, diesel–propane and diesel–methane combustion behaved very similarly, the primary differences being in the preignition chemistry and the ignition delay trends. At a brake mean effective pressure of 2.5 bar, the nitrogen oxide and smoke emissions were simultaneously reduced while the carbon monoxide and total unburned hydrocarbon emissions were increased. At a brake mean effective pressure of 10 bar (a baseline diesel fuel conversion efficiency of 38%), diesel–propane fueling was prone to rapid earlier combustion while diesel–methane combustion was slower. For diesel–methane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency decreased to 37.1% as the percentage energy substitution was increased to 51%. For diesel–propane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency increased to 39% as the percentage energy substitution was increased to 46%. At high-brake-mean-effective-pressure–high-percentage-energy-substitution and large-pilot-quantity–high-equivalence-ratio conditions, diesel–propane combustion showed an apparent departure from the classical three-phase dual-fuel combustion to a distributed volumetric combustion process that resembled a “diesel-regulated homogenous-charge-compression-ignition-like” combustion process.

Analysis of Ignition Behavior in a Turbocharged Direct Injection Dual Fuel Engine Using Propane and Methane as Primary Fuels

Dual fuel engine combustion utilizes a high-cetane fuel to initiate combustion of a low-cetane fuel. The performance and emissions benefits (low NOx and soot emissions) of dual fuel combustion are well-known. Ignition delay (ID) of the injected high-cetane fuel plays a critical role in quality of the dual fuel combustion process. This paper presents experimental analyses of the ID behavior for diesel-ignited propane and diesel-ignited methane dual fuel combustion. Two sets of experiments were performed at a constant engine speed (1800 rev/min) using a four-cylinder direct injection diesel engine with the stock electronic conversion unit (ECU) and a wastegated turbocharger. First, the effects of fuel–air equivalence ratios (Фpilot ∼ 0.2–0.6 and Фoverall ∼ 0.2–0.9) on IDs were quantified. Second, the effects of gaseous fuel percent energy substitution (PES) and brake mean effective pressure (BMEP) (from 2.5 to 10 bars) on IDs were investigated. With constant Фpilot (>0.5), increasing Фoverall with propane initially decreased ID but eventually led to premature propane auto-ignition; however, the corresponding effects with methane were relatively minor. Cyclic variations in the start of combustion (SOC) increased with increasing Фoverall (at constant Фpilot) more significantly for propane than for methane. With increasing PES at constant BMEP, the ID showed a nonlinear trend (initially increasing and later decreasing) at low BMEPs for propane but a linearly decreasing trend at high BMEPs. For methane, increasing PES only increased IDs at all BMEPs. At low BMEPs, increasing PES led to significantly higher cyclic SOC variations and SOC advancement for both propane and methane. Finally, the engine ignition delay (EID), defined as the separation between the start of injection (SOI) and the location of 50% of the cumulative heat release, was also shown to be a useful metric to understand the influence of ID on dual fuel combustion. Dual fuel ID is profoundly affected by the overall equivalence ratio, pilot fuel quantity, BMEP, and PES. At high equivalence ratios, IDs can be quite short, and beyond a certain limit, can lead to premature auto-igniton of the low-cetane fuel (especially for a reactive fuel like propane). Therefore, it is important to quantify dual fuel ID behavior over a range of engine operating conditions.

Performance and Emissions Characteristics of Diesel-Ignited Gasoline Dual Fuel Combustion in a Single-Cylinder Research Engine

Diesel-ignited gasoline dual fuel combustion experiments were performed in a single-cylinder 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 of 1500 rev/min, a constant load of 5.2 bar IMEP, and a constant gasoline energy substitution of 80%. Parameters such as diesel injection timing (SOI), diesel injection pressure, and boost pressure were varied to quantify their impact on engine performance and engine-out ISNOx, ISHC, ISCO, and smoke emissions. Advancing SOI from 30 DBTDC to 60 DBTDC reduced ISNOx from 14 g/kWhr to less than 0.1 g/kWhr; further advancement of SOI did not yield significant ISNOx reduction. A fundamental change was observed from heterogeneous combustion at 30 DBTDC to “premixed enough” combustion at 50–80 DBTDC and finally to well-mixed diesel-assisted gasoline HCCI-like combustion at 170 DBTDC. Smoke emissions were less than 0.1 FSN at all SOIs, while ISHC and ISCO were in the range of 8–20 g/kWhr, 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 for 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.Copyright

Diesel-Ignited Propane Dual Fuel Low Temperature Combustion in a Heavy-Duty Diesel Engine

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.Copyright

Performance and Emissions Characteristics of Diesel-Ignited Gasoline Dual Fuel Combustion in a Single Cylinder Research Engine

Diesel-ignited gasoline dual fuel combustion experiments were performed in a single-cylinder 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 of 1500 rev/min, a constant load of 5.2 bar IMEP, and a constant gasoline energy substitution of 80%. Parameters such as diesel injection timing (SOI), diesel injection pressure, and boost pressure were varied to quantify their impact on engine performance and engine-out ISNOx, ISHC, ISCO, and smoke emissions. Advancing SOI from 30 DBTDC to 60 DBTDC reduced ISNOx from 14 g/kWhr to less than 0.1 g/kWhr; further advancement of SOI did not yield significant ISNOx reduction. A fundamental change was observed from heterogeneous combustion at 30 DBTDC to “premixed enough” combustion at 50–80 DBTDC and finally to well-mixed diesel-assisted gasoline HCCI-like combustion at 170 DBTDC. Smoke emissions were less than 0.1 FSN at all SOIs, while ISHC and ISCO were in the range of 8–20 g/kWhr, 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 for 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.Copyright

Performance and Emissions Characteristics of Bio-Diesel (B100)-Ignited Methane and Propane Combustion in a Four Cylinder Turbocharged Compression Ignition Engine

Different combustion strategies and fuel sources are needed to deal with increasing fuel efficiency demands and emission restrictions. One possible strategy is dual fueling using readily available resources. Propane and natural gas are readily available with the current infrastructure and biodiesel is growing in popularity as a renewable fuel. This paper presents experimental results from dual fuel combustion of methane (as a surrogate for natural gas) and propane as primary fuels with biodiesel pilots in a 1.9 liter, turbocharged, 4 cylinder diesel engine at 1800 rev/min. Experiments were performed with different percentage energy substitutions (PES) of propane and methane and at different brake mean effective pressures (BMEP/bmep). Brake thermal efficiency (BTE) and emissions (NOx, HC, CO, CO2 , O2 and smoke) were also measured. Maximum PES levels for B100-methane dual fuelling were limited to 70% at 2.5 bar bmep and 48% at 10 bar bmep, and corresponding values for B100-propane dual fuelling were 64% and 43%, respectively. Maximum PES was limited by misfire at 2.5 bar bmep and the onset of engine knock at 10 bar bmep. Dual fuel BTEs approached straight B100 values at 10 bar bmep while they were significantly lower than B100 values at 2.5 bar bmep. In general dual fuelling was beneficial in reducing NOx and smoke emissions by 33% and 50%, respectively from baseline B100 levels; however, both CO and THC emissions were significantly higher than baseline B100 levels at all PES and loads.Copyright

Comparison of Propane and Methane Performance and Emissions in a Turbocharged Direct Injection Dual Fuel Engine

With increasingly restrictive NOx and PM emissions standards, the recent discovery of new natural gas reserves, and the possibility of producing propane efficiently from biomass sources, dual fueling strategies have become more attractive. This paper presents experimental results from dual-fueling a four-cylinder turbocharged DI diesel engine with propane or methane (a natural gas surrogate) as the primary fuel and diesel as the ignition source. Experiments were performed with the stock ECU at a constant speed of 1800 rev/min, and a wide range of BMEPs (2.7 to 11.6 bar) and percent energy substitutions (PES) of C3 H8 and CH4 . Brake thermal efficiencies (BTE) and emissions (NOx , smoke, THC, CO, and CO2 ) were measured. Maximum PES levels of about 80–95 percent with CH4 and 40–92 percent with C3 H8 were achieved. Maximum PES was limited by poor combustion efficiencies and engine misfire at low loads for both C3 H8 and CH4 , and the onset of knock above 9 bar BMEP for C3 H8 . While dual fueling BTEs were lower than straight diesel BTEs at low loads, they approached diesel BTE values at high loads. With dual fueling, NOx and smoke reductions (from diesel values) were as high as 66–68 percent and 97 percent, respectively, but CO and THC emissions were significantly higher with increasing PES at all engine loads.© 2010 ASME