Large–squish piston geometry and early pilot injection for high efficiency and low methane emission in natural gas–diesel dual fuel engine at high–load operations

Abstract Dual fuel diesel-methane low temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual fuel LTC typically exhibit poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting the methane combustion once the process is initiated by the first one. In this work, diesel-methane dual fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas surrogate). A multidimensional model is first validated in comparison with experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 CAD and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion emissions are investigated, again showing good agreement with experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline. Furthermore, it is shown that post-injection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

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Option for Adoption of Hydrogen or Natural Gas With Emulsified Biodiesel for Pilot Injection in Dual-Fuel Operation of Diesel Engines

10.2118/150793-ms ◽

2011 ◽

Author(s):

K.D.H. Bob-Manuel ◽

R.J. Crookes ◽

T. Korakianitis ◽

A.M. Namasivayam

Keyword(s):

Natural Gas ◽

Diesel Engines ◽

Dual Fuel ◽

Pilot Injection ◽

Emulsified Biodiesel

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A Numerical Study on the Pilot Injection Conditions of a Marine 2-Stroke Lean-Burn Dual Fuel Engine

Processes ◽

10.3390/pr8111396 ◽

2020 ◽

Vol 8 (11) ◽

pp. 1396

Author(s):

Hao Guo ◽

Song Zhou ◽

Jiaxuan Zou ◽

Majed Shreka

Keyword(s):

Natural Gas ◽

Fuel Injection ◽

Numerical Study ◽

Pollutant Emissions ◽

Dual Fuel ◽

Injection Timing ◽

Pilot Injection ◽

Lean Burn ◽

Injection Duration ◽

Pilot Fuel

The global demand for clean fuels is increasing in order to meet the requirements of the International Maritime Organization (IMO) of 0.5% global Sulphur cap and Tier III emission limits. Natural gas has begun to be popularized on liquefied natural gas (LNG) ships because of its low cost and environment friendly. In large-bore marine engines, ignition with pilot fuel in the prechamber is a good way to reduce combustion variability and extend the lean-burn limit. However, the occurrence of knock limits the increase in power. Therefore, this paper investigates the effect of pilot fuel injection conditions on performance and knocking of a marine 2-stroke low-pressure dual-fuel (LP-DF) engine. The engine simulations were performed under different pilot fuel parameters. The results showed that the average in-cylinder temperature, the average in-cylinder pressure, and the NOx emissions gradually decreased with the delay of the pilot injection timing. Furthermore, the combustion situation gradually deteriorated as the pilot injection duration increased. A shorter pilot injection duration was beneficial to reduce NOx pollutant emissions. Moreover, the number of pilot injector orifices affected the ignition of pilot fuel and the flame propagation speed inside the combustion chamber.

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

Frontiers in Mechanical Engineering ◽

10.3389/fmech.2020.545416 ◽

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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