Theoretical Analyses of Heat Balance in a Diesel/Natural Gas Dual-Fuel Engine at Low and Medium Loads Based on Experimental Values

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Zhongshu Wang ◽  
Guizhi Du ◽  
Ming Li ◽  
Yun Xu ◽  
Fangyuan Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Gas ◽  
Thermal Efficiency ◽  
Hot Water ◽  
Energy Utilization ◽  
Dual Fuel ◽  
Exergy Destruction ◽  
Energy Fraction ◽  
Combustion Heat ◽  
Diesel Injection

Abstract In order to propose the control strategies based on exergy to realize efficient and energy-saving operation of the engine, the energy and exergy balance under sensitive boundary conditions were analyzed with the first and second laws of thermodynamics on a six-cylinders, four strokes, turbocharged, intercooled, and high-pressure common rail diesel/natural gas (NG) dual-fuel engine in this paper. The results depicted that the thermal efficiency and exergy efficiency decrease with the increase of NG percentage energy substitution rate (PES). Compared with other conditions, at medium load, 1978 rpm and 90% PES, the exergy destruction caused by irreversibility process including mixing combustion, heat transfer and mechanical friction reaches 72.33%. With the advance of diesel injection time (Tinj), thermal efficiency and energy fraction of heat transfer increase first and then decrease. However, diesel injection pressure (Pinj) has little effect on improving energy utilization. Compared with single diesel injection, appropriate multiple diesel injection can improve combustion performance and energy utilization. When the first Tinj is 35 deg CA BTDC and second Tinj is 25 deg CA BTDC, nearly 50% of the energy lost in heat transfer can be converted into useful work. The lost exergy can be reduced by choosing appreciate Tinj and Pinj, adding exhaust gas recirculation (EGR) to reduce in-cylinder temperature to improve combustion and using thermal insulation materials to reduce heat transfer or using the lost heat in other processes such as preheating intake air and producing the hot water or steam of external consumption to reduce the exergy destruction.

Numerical optimization of natural gas and diesel dual-fuel combustion for a heavy-duty engine operated at a medium load

2017 ◽  
Vol 19 (6) ◽  
pp. 682-696 ◽  
Author(s):  
Zhenkuo Wu ◽  
Christopher J Rutland ◽  
Zhiyu Han
Keyword(s):  
Genetic Algorithm ◽  
Natural Gas ◽  
Thermal Efficiency ◽  
Single Injection ◽  
Dual Fuel ◽  
Heavy Duty ◽  
Algorithm Optimization ◽  
Injection Strategy ◽  
Diesel Injection ◽  
Dual Fuel Combustion

In this study, natural gas and diesel dual-fuel combustion under a medium load was numerically optimized for a heavy-duty engine using a genetic algorithm optimization approach. This approach employed a micro-genetic algorithm optimization code coupled with an engine computational fluid dynamics code to perform the optimization. Initially, an optimization using premixed natural gas with double direct injection of diesel fueling strategy was conducted using both the stock piston bowl shape and a bathtub shaped piston. Low emissions and moderate combustion with thermal efficiency close to 50% were achieved for both piston configurations by optimizing the premixed natural gas to diesel fuel ratio, exhaust gas recirculation fraction, diesel injection timing, injection pressure, and injection split ratio. Based on this optimum point, a parametric study was performed to understand the effects of the optimization parameters. The results show that high efficiency and clean combustion (indicated thermal efficiency ≥ 45%, NOx ≤ 0.4 g/kW h, peak pressure rise rate ≤ 15 bar/°) can be achieved over a wide range of parameters. The optimized result of a single diesel injection strategy was also evaluated and compared with the double injection strategy. The results indicate that the single injection strategy is also able to yield near 50% thermal efficiency and clean combustion. Compared to the double injection strategy, the single injection strategy shows increased combustion losses due to reduced diesel fuel near the cylinder centerline. In addition, the bathtub shaped piston has lower heat transfer losses relative to the stock piston, leading to improved fuel efficiency. However, the piston shape shows less impact than other parameters on the overall combustion and emission characteristics for both injection strategies.

scholarly journals Cyclic Combustion Variations in Dual Fuel Partially Premixed Pilot-Ignited Natural Gas Engines

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
K. K. Srinivasan ◽  
S. R. Krishnan ◽  
Y. Qi
Keyword(s):  
Natural Gas ◽  
Dual Fuel ◽  
Nox Emissions ◽  
Natural Gas Engines ◽  
Percentage Points ◽  
Combustion Modes ◽  
Diesel Injection ◽  
Cyclic Variations ◽  
Partially Premixed ◽  
Dual Fueling

Dual fuel pilot-ignited natural gas engines are identified as an efficient and viable alternative to conventional diesel engines. This paper examines cyclic combustion fluctuations in conventional dual fuel and in dual fuel partially premixed combustion (PPC). Conventional dual fueling with 95% (energy basis) natural gas (NG) substitution reduces NOx emissions by almost 90% relative to neat diesel operation; however, this is accompanied by 98% increase in HC emissions, 10 percentage points reduction in fuel conversion efficiency (FCE) and 12 percentage points increase in COVimep. Dual fuel PPC is achieved by appropriately timed injection of a small amount of diesel fuel (2–3% on an energy basis) to ignite a premixed natural gas–air mixture to attain very low NOx emissions (less than 0.2 g/kWh). Cyclic variations in both combustion modes were analyzed by observing the cyclic fluctuations in start of combustion (SOC), peak cylinder pressures (Pmax), combustion phasing (Ca50), and the separation between the diesel injection event and Ca50 (termed “relative combustion phasing”). For conventional dual fueling, as NG substitution increases, Pmax decreases, SOC and Ca50 are delayed, and cyclic variations increase. For dual fuel PPC, as diesel injection timing is advanced from 20 deg to 60 deg BTDC, Pmax is observed to increase and reach a maximum at 40 deg BTDC and then decrease with further pilot injection advance to 60 deg BTDC, the Ca50 is progressively phased closer to TDC with injection advance from 20 deg to 40 deg BTDC, and is then retarded away from TDC with further injection advance to 60 deg BTDC. For both combustion modes, cyclic variations were characterized by alternating slow and fast burn cycles, especially at high NG substitutions and advanced injection timings. Finally, heat release return maps were analyzed to demonstrate thermal management strategies as an effective tool to mitigate cyclic combustion variations, especially in dual fuel PPC.

scholarly journals Use of Adaptive Injection Strategies to Increase the Full Load Limit of RCCI Operation

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Reed Hanson ◽  
Andrew Ickes ◽  
Thomas Wallner
Keyword(s):  
Natural Gas ◽  
Thermal Efficiency ◽  
Fuel Injection ◽  
Experimental Testing ◽  
Peak Load ◽  
Combustion Process ◽  
Pressure Rise ◽  
Dual Fuel ◽  
The Impact ◽  
Injection Strategies

Dual-fuel combustion using port-injection of low reactivity fuel combined with direct injection (DI) of a higher reactivity fuel, otherwise known as reactivity controlled compression ignition (RCCI), has been shown as a method to achieve low-temperature combustion with moderate peak pressure rise rates, low engine-out soot and NOx emissions, and high indicated thermal efficiency. A key requirement for extending to high-load operation is moderating the reactivity of the premixed charge prior to the diesel injection. One way to accomplish this is to use a very low reactivity fuel such as natural gas. In this work, experimental testing was conducted on a 13 l multicylinder heavy-duty diesel engine modified to operate using RCCI combustion with port injection of natural gas and DI of diesel fuel. Engine testing was conducted at an engine speed of 1200 rpm over a wide variety of loads and injection conditions. The impact on dual-fuel engine performance and emissions with respect to varying the fuel injection parameters is quantified within this study. The injection strategies used in the work were found to affect the combustion process in similar ways to both conventional diesel combustion (CDC) and RCCI combustion for phasing control and emissions performance. As the load is increased, the port fuel injection (PFI) quantity was reduced to keep peak cylinder pressure (PCP) and maximum pressure rise rate (MPRR) under the imposed limits. Overall, the peak load using the new injection strategy was shown to reach 22 bar brake mean effective pressure (BMEP) with a peak brake thermal efficiency (BTE) of 47.6%.

Combustion phase of a diesel/natural gas dual fuel engine under various pilot diesel injection timings

Fuel ◽  
2021 ◽  
Vol 289 ◽  
pp. 119869
Author(s):  
Zhongshu Wang ◽  
Fangyuan Zhang ◽  
Ye Xia ◽  
Dan Wang ◽  
Yun Xu ◽  
...  
Keyword(s):  
Natural Gas ◽  
Dual Fuel ◽  
Diesel Injection ◽  
Combustion Phase

scholarly journals Cyclic Combustion Variations in Dual Fuel Partially Premixed Pilot-Ignited Natural Gas Engines

2012 ◽  
Author(s):  
K. K. Srinivasan ◽  
S. R. Krishnan ◽  
Y. Qi
Keyword(s):  
Natural Gas ◽  
Dual Fuel ◽  
Nox Emissions ◽  
Natural Gas Engines ◽  
Percentage Points ◽  
Combustion Modes ◽  
Diesel Injection ◽  
Cyclic Variations ◽  
Partially Premixed ◽  
Dual Fueling

Dual fuel pilot ignited natural gas engines are identified as an efficient and viable alternative to conventional diesel engines. This paper examines cyclic combustion fluctuations in conventional dual fuel and in dual fuel partially premixed low temperature combustion (LTC) at 1700 rev/min and 6 bar brake mean effective pressure (bmep). Conventional dual fueling with 95% (energy basis) natural gas (NG) substitution reduces NOx emissions by almost 90%t relative to straight diesel operation; however, this is accompanied by 98% increase in HC emissions, 10 percentage points reduction in fuel conversion efficiency (FCE) and 12 percentage points increase in COVimep. Dual fuel LTC is achieved by injection of a small amount of diesel fuel (2–3 percent on an energy basis) to ignite a premixed natural gas–air mixture to attain very low NOx emissions (less than 0.2 g/kWh). Cyclic variations in both combustion modes were analyzed by observing the cyclic fluctuations in start of combustion (SOC), peak cylinder pressures (Pmax), combustion phasing (Ca50), and the separation between the diesel injection event and Ca50 (termed “relative combustion phasing”). For conventional dual fueling, as % NG increases, Pmax decreases, SOC and Ca50 are delayed, and cyclic variations increase. For dual fuel LTC, as diesel injection timing is advanced from 20° to 60°BTDC, the relative combustion phasing is identified as an important combustion parameter along with SoC, Pmax, and CaPmax. For both combustion modes, cyclic variations were characterized by alternating slow and fast burn cycles, especially at high %NG and advanced injection timings. Finally, heat release return maps were analyzed to demonstrate thermal management strategies as an effective tool to mitigate cyclic combustion variations, especially in dual fuel LTC.

scholarly journals A Study on the High Load Operation of a Natural Gas-Diesel Dual-Fuel Engine

2020 ◽  
Vol 6 ◽  
Author(s):  
Shouvik Dev ◽  
Hongsheng Guo ◽  
Brian Liko
Keyword(s):  
Particulate Matter ◽  
Natural Gas ◽  
Diesel Engines ◽  
Thermal Efficiency ◽  
Direct Injection ◽  
High Load ◽  
Dual Fuel ◽  
Nox Emissions ◽  
Brake Thermal Efficiency ◽  
Dual Fuel Engines

Diesel fueled compression ignition engines are widely used in power generation and freight transport owing to their high fuel conversion efficiency and ability to operate reliably for long periods of time at high loads. However, such engines generate significant amounts of carbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM) emissions. One solution to reduce the CO2 and particulate matter emissions of diesel engines while maintaining their efficiency and reliability is natural gas (NG)-diesel dual-fuel combustion. In addition to methane emissions, the temperatures of the diesel injector tip and exhaust gas can also be concerns for dual-fuel engines at medium and high load operating conditions. In this study, a single cylinder NG-diesel dual-fuel research engine is operated at two high load conditions (75% and 100% load). NG fraction and diesel direct injection (DI) timing are two of the simplest control parameters for optimization of diesel engines converted to dual-fuel engines. In addition to studying the combined impact of these parameters on combustion and emissions performance, another unique aspect of this research is the measurement of the diesel injector tip temperature which can predict potential coking issues in dual-fuel engines. Results show that increasing NG fraction and advancing diesel direct injection timing can increase the injector tip temperature. With increasing NG fraction, while the methane emissions increase, the equivalent CO2 emissions (cumulative greenhouse gas effect of CO2 and CH4) of the engine decrease. Increasing NG fraction also improves the brake thermal efficiency of the engine though NOx emissions increase. By optimizing the combustion phasing through control of the DI timing, brake thermal efficiencies of the order of ∼42% can be achieved. At high loads, advanced diesel DI timings typically correspond to the higher maximum cylinder pressure, maximum pressure rise rate, brake thermal efficiency and NOx emissions, and lower soot, CO, and CO2-equivalent emissions.

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