Using traditional welding methods, rocket engine nozzles and combustion chambers are some of the most difficult parts to fabricate, requiring up to a year to produce a single part. Now, however, the U.S. National Aeronautics and Space Administration (NASA) is using additive manufacturing technology, also known as 3D printing, to additively build those parts, layer upon layer. This technology differs completely from traditional manufacturing methods that manufacture destructively by taking away material until a final geometry is realized. 3D printing has allowed NASA to produce rocket engine nozzles with integrated cooling channels in 30 days by way of an additive process called blown powder directed energy deposition (BP-DED). See also: Nozzle; Rocket propulsion; 3D printing

During the past decade, the automotive industry has converted more than 50 percent of its internal combustion engines from a traditional technology called port fuel injection (PFI) to a new technology called gasoline direct injection (GDI). The fundamental difference between the two engine types is that GDI engines inject fuel directly into the combustion chamber instead of the injection port of the PFI engine. Benefits of GDI technology—improved fuel economy, lower carbon dioxide (CO₂) emissions, and increased power output—have resulted in rapid adoption. By 2025, the U.S. Environmental Protection Agency (EPA) projects that 93 percent of all vehicles produced will use GDI engines. However, the downside of direct fuel injection, according to a recent report in the journal Environmental Science & Technology, is a high level of black carbon (BC) aerosol emissions, which adversely affects both climate and public health. See also: Aerosol; Automobile; Carbon black; Fuel injection; Gasoline; Internal combustion engine

A study published in the journal Atmospheric Environment (April 2019), comparing the differences in air pollution caused by automobiles powered by internal combustion (conventional) engines versus electric vehicles (EVs) powered by batteries, reported that EVs improve air quality even when the electricity used to power them was generated by non-renewable combustion power plants. The study was based on air-quality simulations modeling emissions from automobiles and power plants of ozone and particulate matter—two noxious compounds found in smog that are associated with respiratory health problems. See also: Air pollution; Automobile; Battery; Electric vehicle; Internal combustion engine; Ozone; Particulates; Power plant; Respiratory system disorders; Simulation; Smog

Despite the cost-saving advantages of low maintenance and high fuel economy, most battery-powered electric vehicles (EVs) have a limited driving range of about 80 miles (130 kilometers). Not surprisingly, one of the biggest obstacles to consumer acceptance of EVs is range anxiety—the fear of running out of battery power before completing a trip or reaching a charging station. This anxiety can lead EV owners to drive less as a precaution, even though most people would normally drive distances per day that are well within an EV’s fully charged range. See also: Automobile; Electric vehicle

Many new-model electric vehicles (EVs) now have a driving range greater than 320 kilometers (200 miles). Consequently, range anxiety—the fear of running out of battery power before completing a trip or reaching a charging station—is becoming less problematic. Battery charging, however, remains an issue, as it may take as long as eight hours to recharge an EV battery to its full capacity. Nevertheless, thanks to advances in battery technology, a number of new and existing battery suppliers are reporting EV battery packs in late stages of development that can accept a full charge in 10 to 15 minutes. See also: Battery; Electric vehicle; Electric vehicles and range anxiety

Although international shipping is critical to global trade, cargo ships are a major source of air pollution, including greenhouse gas emissions. At present, atmospheric emissions from fuel oil-powered marine ships include sulfur oxides (SO_x), nitrogen oxides (NO_x), particulate matter (PM), and carbon dioxide (CO₂). According to the International Maritime Organization (IMO), the United Nations agency responsible for preventing air pollution by ships, maritime shipping is responsible for 18 to 30 percent of NO_x, 9 percent of SO_x, and 3.5 to 4 percent of CO₂ emissions worldwide. In addition, the maritime risk management and environmental assessment organization RightShip projects that if no abatement action is taken, global CO₂ emissions may increase 50 to 250 percent by 2050 because of shipping growth. In April 2018, the IMO adopted a non-binding agreement to reduce CO₂ emissions. Suggested carbon reduction strategies include improving fuel quality and engine emission standards as well as using new technologies, such as fuel cells, biofuels, and advanced sail design. See also: Air pollution; Biosynthesis of fuels; Carbon dioxide; Fuel oil; Nitrogen oxides; Ship powering, maneuvering, and seakeeping

To understand how much land the average solar power plant occupies, the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) analyzed the land-use requirements in 2012 for 72% of the operating utility-scale photovoltaic (PV) and concentrating solar power (CSP) plants in the United States. Utility-scale solar plants are those with capacities greater than 1 megawatt (MW). Comparing the total land area (fenced-in area) of CSP and PV plants and normalizing the values for alternating-current (ac; PV is direct current), the NREL found that 25 CSP plants with a total capacity of 3747 MW used on average 10 acres/MWac, whereas 147 PV plants with a total capacity of 4100 MW used on average 8.9 acres/MWac. See also: Concentrating solar power; Electric power generation; Energy sources; Solar cell; Solar energy

Naturally ventilating a house, such as by opening doors and windows, has long been considered an effective strategy for exhausting indoor air pollutants. However, according to researchers reporting in the journal Science Advances (February 2020), that assumption may be incorrect. The researchers observed that opening doors and windows reduced air-pollutant levels, but only temporarily. Within a few minutes after closing all doors and windows, pollutant levels returned to non-ventilated (original) levels. Why? As it turns out, indoor air pollutants are not just airborne, as are many outdoor air pollutants. Indoor air pollutants are attracted to solid surfaces to which the particles can easily attach, and from which they can subsequently detach. See also: Air pollution; Indoor air pollution; Ventilation

In the short term, the future of autonomous-vehicle technology is hard to unravel, but two reports (May 2017) offer some insight into what we might expect. A multidisciplinary research team from eight universities reported in the e-print repository arXiv how automated vehicles affect traffic flow. The research team found that on a test track, which mimicked a single-lane stretch of road, when one out of 21 or 22 vehicles (about 5 percent) was automatically controlled, researchers could eliminate stop-and-go waves, known as "phantom traffic jams." The team accomplished this by adjusting the automated vehicle’s (AV) speed and distance from the vehicle in front of it, and by estimating the average speed of the vehicles in front of the AV. In addition to controlling traffic flow, having an AV in the mix reduced braking and fuel consumption. Based on the simplicity of their control strategy, the researchers concluded that even though self-driving cars are years away from acceptance, implementing similar controls in available technology, such as adaptive cruise control, intelligent infrastructure, and connected vehicles, could reduce congestion in traffic flow. See also: Connected vehicles; Intelligent transportation systems; Intelligent vehicles and infrastructure; Intervehicle communications; Self-driving cars; Transportation engineering

Internal combustion engines are very inefficient at converting chemical energy to mechanical energy. Among the energy losses are friction and heat losses. In October 2016, researchers from the Georgia Institute of Technology, Atlanta, United States, and Technion–Israel Institute of Technology, Haifa, Israel demonstrated a process for reducing the energy losses due to friction by chemically and mechanically modifying the surfaces of metal parts. This process could potentially be used for friction reduction in automotive engines. See also: Energy conversion; Engine; Friction; Internal combustion engine; Tribology