October - December 1998

Straw-Based Insulation for Pakistan:
Addressing the Needs of Developing Regions
[Abstract] [References]

Direct-Injection Automotive Engines: New Insights for Designers
[Abstract] [References]

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Straw-Based Insulation for Pakistan: Addressing the Needs of Developing Regions

n remote, mountainous regions of northern Pakistan, buildings are typically made of uninsulated stone or cement block. Wood and other fuels are scarce, and indoor temperatures in winter are frequently only a few degrees above those outdoors. A straw-based insulation developed by Energy Laboratory researchers in MIT's Building Technology Program could help boost those temperatures while saving fuel. Drawing on a technique developed by ICI Polyurethanes, the researchers place milled straw inside a tumbler with a central nozzle that sprays fine droplets of an adhesive onto the tumbling straw. Once coated, the straw is removed, placed in a frame, and pressed and heated. The straw boards produced can be installed on interior walls; and they have the insulating value of expanded polystyrene, the only other rigid insulation available in Pakistan. Half the cost of polystyrene, the straw insulation could be made in local factories using local materials, simple machinery, and little energy. Only small amounts of adhesive would have to be imported. Case studies at four Pakistani schools show that installing straw insulation could cut energy requirements by half or more. The methods developed here could be applied in many developing areas using straw or other available waste materials.

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Direct-Injection Automotive Engines: New Insights for Designers

ew vehicles with direct-injection spark-ignited (DISI) gasoline engines offer high power and fuel efficiencies fully 30% higher than those of conventional gasoline engines. The high efficiency of DISI engines stems from their ability to run "fuel lean," that is, with a lower fuel-to-air ratio than used in conventional engines. Smooth ignition, however, requires a relatively "fuel-rich" mixture. The challenge in DISI engines is therefore to capitalize on the lean part while ensuring a strong fuel-air mixture at the spark plug. To provide adequate fuel vaporization and transport to the ignition source, many designs use high-pressure fuel injectors that provide swirl to the liquid fuel as it enters the combustion chamber, creating a hollow cone of droplets that stays airborne long enough to vaporize. However, Energy Laboratory experiments in a transparent test engine show that the injected fuel may not always form a hollow cone. When fuel temperatures are high or pressures in the combustion chamber are low, the hollow cone can become filled in and more jet-like--especially when the burning mixture contains components with low boiling points, as does gasoline. The researchers' explanation? When the mixture enters the combustion chamber, the low-boiling-point components suddenly vaporize with enough force to shatter the liquid film. The tiny droplets that result are sucked into the center of the disintegrating hollow cone. The MIT research findings should help engine designers optimize the geometry of the combustion chamber to ensure complete vaporization and easy ignition under all engine conditions.

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