LNG Fuel Differentiation: DME/LNG Blends for HPDI Engines

Abstract

<div class="section abstract"><div class="htmlview paragraph">With increased awareness and scrutiny of greenhouse gas (GHG) emissions, the heavy-duty truck industry is on the lookout for solutions that can maximize GHG savings, through either lowering fuel consumption and lowering methane slip. This paper focuses on whether it is possible to provide a differentiated Liquefied Natural Gas (LNG) that supports the further improvement of a High-Pressure Direct Injection (HPDI) Engine. Desired improvements from this LNG blend are the lowering or substitution of the pilot Diesel use of the current HPDI engine, the lowering of the raw exhaust gas methane concentration and any additional performance improvements. Sixty-five substances were identified that could potentially be blended into cryogenic methane thus creating a differentiated LNG fuel. This paper goes through the process of additive selection and then focuses primarily on the results for using Dimethyl Ether (DME) as an LNG component, one of the candidate substances, but also showcases some of the other potential additives.</div><div class="htmlview paragraph">To study the autoignition properties of DME/LNG blends, autoignition delay times were simulated and then measured in a Rapid Compression Machine at engine conditions. The results were used to optimize the chemical mechanism that is used as input into a High-Pressure Direct Injection engine model. It was found that more than 5 vol% DME is required to reach a significant reduction in the autoignition delay time at typical operating conditions. The engine modelling results were also used to determine the initial conditions for HDPI engine tests using a modified 15L-Westport engine.</div><div class="htmlview paragraph">These engine tests showed that an LNG/DME blend could potentially be used to develop a mono-fuel HPDI engine. However, it was found that although the mono-fuel concept works for high load conditions with the existing HPDI engine, further research is needed to enable stable combustion at lower loads and idling while keeping DME proportions at levels that could be dissolved in LNG. It was also found that higher proportions of DME in the LNG could lead to a reduction of the methane slip.</div></div>

Autoignition enhancement of methane by admixture of low fraction of acetaldehyde: Simulations and RCM experiments in stoichiometric and rich mixtures

“…The excellent knock resistance of methane makes natural gas (consisting predominantly of methane) and its renewable replacement, biomethane (e.g., via the anaerobic digestion of biomass 1 ), very suitable fuels for spark-ignited (SI) engines. 2 At the same time, this resistance to autoignition under engine conditions excludes its use for engines that rely on compression ignition (CI), such as diesel engines, without the use of a pilot fuel for ignition (see, e.g., 3 ). Adding small quantities of an ignition enhancer to natural gas/biomethane to facilitate CI would permit its use in diesel-type engines, which have significantly higher efficiencies than SI engines.…”

“…A range of different promoters has been investigated in rapid compression machines (RCMs) and shock tubes. [3][4][5][6][7][8][9] The ignition properties of methane with various fuels, such as H 2 (e.g., at 10-70 bar and 960-1060 K 6 ), higher alkanes, for example, ethane (25-50 bar and 900-1050 K 7 ), and diesel fuel (6-20 bar and 640-1450 K 5 ), have been reported. Oxygenated species have also been studied, such as dimethyl ether (DME) (60 bar and 700-900 K 3 and 7-41 atm and 600-1600 K in RCM and shock tube 4 ), ethanol and n-propanol (3-10 atm and 1100-1500 K in a shock tube 9 ), and methyl propanoate (4-10 atm and 1000-1500 K in a shock tube 8 ).…”

“…Adding small quantities of an ignition enhancer to natural gas/biomethane to facilitate CI would permit its use in diesel‐type engines, which have significantly higher efficiencies than SI engines. Combined with the potential for reduced methane slip 3 as compared to SI engines, use of methane‐based fuels in efficient CI engines can reduce the CO 2 footprint of the utilization of these fuels.…”

“…The ignition enhancement of methane by other fuel components has been examined in studies under engine‐relevant conditions. A range of different promoters has been investigated in rapid compression machines (RCMs) and shock tubes 3–9 . The ignition properties of methane with various fuels, such as H 2 (e.g., at 10–70 bar and 960–1060 K 6 ), higher alkanes, for example, ethane (25–50 bar and 900–1050 K 7 ), and diesel fuel (6–20 bar and 640–1450 K 5 ), have been reported.…”

“…The ignition properties of methane with various fuels, such as H 2 (e.g., at 10–70 bar and 960–1060 K 6 ), higher alkanes, for example, ethane (25–50 bar and 900–1050 K 7 ), and diesel fuel (6–20 bar and 640–1450 K 5 ), have been reported. Oxygenated species have also been studied, such as dimethyl ether (DME) (60 bar and 700–900 K 3 and 7–41 atm and 600–1600 K in RCM and shock tube 4 ), ethanol and n ‐propanol (3–10 atm and 1100–1500 K in a shock tube 9 ), and methyl propanoate (4–10 atm and 1000–1500 K in a shock tube 8 ). The oxygenated compounds exhibit ignition delay times nearly two orders of magnitude shorter than that of methane and the addition of these fuels substantially decreases the ignition delay time of methane.…”