Alcohol lean burn in heavy duty engines: Achieving 25 bar IMEP with high efficiency in spark ignited operation

Abstract

Knock is the most crucial limitation in attaining the peak load required at high efficiency in heavy duty (HD) spark ignition (SI) engines. Renewable fuels such as ethanol and methanol have high resistance to autoignition and can help overcome this limitation. To reduce knock and improve efficiency further, dilution can be used to add specific heat capacity and reduce combustion temperature. This work studied diluted combustion and knock characteristics of gasoline, ethanol, and methanol on a HD SI single cylinder engine for a wide load range. Ethanol and methanol displayed excellent knock resistance which allowed a peak gross IMEP of 25.1 and 26.8 bar respectively, compared to gasoline which only reached 8.3 bar at [Formula: see text]1.4 with a compression ratio of 13. Over 18% increase in gross IMEP was possible for gasoline and ethanol when increasing air excess ratio from 1 to 1.4. Methanol achieved the target gross IMEP at [Formula: see text]1 and required no spark retard at [Formula: see text]1.6. A peak indicated efficiency above 48% was recorded for ethanol and methanol at [Formula: see text]1.6 and gross IMEP of approximately 21 bar. At part loads, stable operation was possible until [Formula: see text]1.8 for all fuels. Increase in intake temperature showed a marginal improvement in stability but no increase in lean limit. The concept shows promise as diluted combustion of ethanol and methanol reduced knock and achieved diesel baseline load. With optimization, there is potential to improve efficiency further and possible cost savings compared to commercial diesel engines.

The Effect of Pure Oxygenated Biofuels on Efficiency and Emissions in a Gasoline Optimised DISI Engine

“…Cairns et al reported increased efficiencies for butanol and ethanol blends in a DISI engine where fuel injection was optimised for the blends [29]. Moreover, the same fuels (gasoline, methanol and ethanol) as used in this study showed great potential as fuel alternatives also in HD SI application [36]. The results in that study were run at a higher compression ratio (13) and thus, more optimised for ethanol and methanol than for gasoline.…”

“…Moreover, several researchers report brake thermal efficiency for ethanol and methanol of 36 to 40% compared to 27 to 36% for gasoline [15,34]. Methanol and ethanol have also shown potential as fuels for heavy-duty (HD) SI application, where similar load and efficiency as HD diesel combustion could be reached with lean combustion of methanol and ethanol [36]. Sileghem et al showed increased efficiency in comparison to gasoline in a DISI engine fuelled with iso-butanol [15].…”

The Impact of Miller Valve Timing on Combustion and Charging Performance of an Ethanol- and Methanol-Fueled Heavy-Duty Spark Ignition Engine

“…In an earlier experiment [ 14 ], 25 bar IMEP was achieved using ethanol and methanol in a HD SI single-cylinder research engine. e engine used PFI and a central spark plug.…”

“…Alcohols' high resistance to end-gas autoignition (knock) aids in increased boosting and e ciency when compared to gasoline in SI operation [ 13 ]. In a recent study [ 14 ], a target load of 25 bar IMEP was achieved using ethanol and methanol on a port fuel-injected HD SI engine. Ethanol, however, was knock limited and required dilution using excess air to reach the target IMEP.…”

“…Ethanol, however, was knock limited and required dilution using excess air to reach the target IMEP. Forty-eight percent gross indicated e ciency was possible using port fuel injection (PFI) SI ethanol [ 14 ], whereas ethanol-diesel dual fuel mixing controlled combustion achieved 50% gross indicated e ciency [ 11 ] at around 20 bar IMEP. Although the target IMEP was achieved with good e ciency using SI combustion, there is potential to bridge the e ciency gap to mixing controlled combustion.…”