Browse Publications Technical Papers 2017-01-0665
2017-03-28

The Competing Chemical and Physical Effects of Transient Fuel Enrichment During Heavy Knock in an Optical SI Engine Using Ethanol Blends 2017-01-0665

The experimental work was concerned with improving understanding of the competing effects of the latent heat of vaporization and auto-ignition delay times of different ethanol blended fuels during heaving knocking combustion. The unique single cylinder SI engine employed included full bore overhead optical access capable of withstanding unusually high in-cylinder pressures. Heavy knock was deliberately induced under moderate loads using inlet air heating and a primary reference fuel blend of reduced octane rating. High-speed chemiluminescence imaging and simultaneous in-cylinder pressure data measurement were used to evaluate the combustion events. Under normal operation the engine was operated under port fuel injection with a stoichiometric air-fuel mixture. Multiple centered auto-ignition events were regularly observed, with knock intensities of up to ~40bar. Additional excess fuel of varied blend was then introduced directly into the end-gas in short transient bursts. As the mass of excess fuel was progressively increased a trade-off was apparent, with knock intensity first increasing by up to 60% before lower unburned gas temperatures suppressed knock under extremely rich conditions. This trade-off is not usually observed during conventional low intensity knock suppression via over-fuelling and has been associated with the reducing auto-ignition delay times outweighing the influence of charge cooling and ratio of specific heats. Ethanol has the highest latent heat of vaporization amongst the other fuels directly injected and was more effective to reduce knock intensity albeit still aggravating knock under slightly rich conditions. Overall, the results demonstrate the risks in employing excess fuel to suppress knock deep within a heavy knocking combustion regime (potentially including a Super-Knock regime).

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Members save up to 18% off list price.
Login to see discount.
Special Offer: Download multiple Technical Papers each year? TechSelect is a cost-effective subscription option to select and download 12-100 full-text Technical Papers per year. Find more information here.
We also recommend:
TECHNICAL PAPER

A 1-D Platform to Simulate the Effects of Dedicated EGR on SI Engine Combustion

2017-01-0524

View Details

JOURNAL ARTICLE

Charge Cooling Effects on Knock Limits in SI DI Engines Using Gasoline/Ethanol Blends: Part 2-Effective Octane Numbers

2012-01-1284

View Details

TECHNICAL PAPER

Modeling of Trace Knock in a Modern SI Engine Fuelled by Ethanol/Gasoline Blends

2015-01-1242

View Details

X