Despite their need for stronger components, diesel engines are generally heavier than petrol engines of the same size, which can negatively impact their performance. Although turbo diesel engines may have a greater horsepower boost, they do not necessarily surpass turbocharged gasoline engines with equivalent boost levels and sizes. Unlike petrol engines, diesel engines are simpler as they lack an ignition system. However, this simplicity does not always result in an advantage as diesel engines can be noisy and require more frequent maintenance intervals.
Diesel engines are renowned for their superior torque, allowing them to handle heavier loads and travel longer distances. As a result, diesel engines are frequently utilized in trucks, pickups, and vehicles used for transporting sizable cargo or with high towing capacities. In contrast, petrol engines generally possess greater horsepower, rendering them faster when compared to diesel engines. Hence, a 2500 cc petrol engine will cover a quarter-mile distance in less time and accelerate from standstill to 60mph more rapidly than its diesel equivalent.
Despite producing less carbon monoxide in its exhaust than petrol engines, diesel engines still emit black soot and aerosols. Nevertheless, utilizing a turbocharger enables a diesel engine to attain comparable performance to a gasoline engine. This allows it to maintain the advantages of superior fuel efficiency over smaller petrol engines, while also experiencing a notable boost in speed.
Common rail technology has improved both diesel and petrol engines, making them more comparable in terms of speed, quietness, and refinement. While commonly associated with diesel engines, common rail technology is also used to enhance petrol engines. Although diesel engines may be preferred for heavy-duty or commercial purposes, if budget is not a concern, I believe that petrol engines provide a smoother driving experience.
There are excellent diesel engines in certain luxury models, but when comparing petrol and diesel, the petrol versions generally outperform them. However, opting for a turbo would be a better choice due to the diesel engine’s inherent low end torque. The turbo would provide more power at higher rpm, where the diesel engine is typically weaker. Supercharging it would enhance low-end power but weaken the top end, resulting in a reverse effect similar to severe turbo lag. (Source: http://www.howstuffworks.com/gasoline2.htm) Gasoline is derived from crude oil.
The black liquid extracted from the ground is called petroleum, which contains hydrocarbons. The carbon atoms in crude oil create chains of different lengths. Diesel fuel has been more costly than gasoline since September 2004, contrary to the typical trend where diesel prices are usually lower than gasoline prices, except during cold winters when demand for heating oil raises diesel prices.
Source: http://www.eia.gov/tools/faqs/faq.cfm?id=9&t=5.
The high prices of diesel fuel compared to gasoline are due to several factors. One factor is the strong global demand for diesel fuel and other distillate fuel oils, which has been particularly high in Europe, China, India, and the United States. This increased demand has coincided with limited worldwide refining capacity during a period of significant economic growth from 2002 to mid-2008. Furthermore, the shift towards cleaner and lower-sulfur diesel fuels in the United States has affected both the production and distribution costs of diesel fuel.
The Federal excise tax for on-highway diesel fuel is 24.4 cents/gallon, which is 6 cents per gallon higher than the gasoline tax. According to this source, historically diesel fuel used in commercial trucks hasn’t always been more expensive than standard gasoline used in passenger vehicles. In theory, diesel fuel should be cheaper to produce than gasoline because it is a less refined petroleum distillate.
The primary concern regarding the cost of diesel fuel primarily stems from the supply and demand dynamics of various petroleum products, rather than the actual production cost. Crude oil can be categorized into different products, including home heating oil, gasoline, kerosene, and more. However, due to limitations in processing all these products simultaneously, oil refiners must prioritize those with higher demand. As a result, commercial vehicle diesel fuel tends to receive lower priority compared to passenger vehicle gasoline.
When diesel fuel supply is low, its price rises. At a specific time annually, oil refiners prioritize producing home heating oil which is similar to diesel fuel. Usually, right before winter arrives, the availability of diesel fuel increases and its price drops. However, this pattern may not always hold as an extremely cold winter can keep the demand for home heating oil high and cause a reduction in diesel fuel production by refiners.
In recent years, the federal government has implemented regulations regarding the acceptable sulfur level in diesel fuel. Refiners are required to meet these regulations and produce ultra low sulfur diesel fuel. Compliance involves substantial investments in new technology and multiple distillations to meet government inspection standards. These additional regulations and advanced equipment can result in significant expenses, often leading to higher prices for consumers.
Critics argue that the government’s preference for imposing heavier taxes on commercial drivers is evident in the disproportionately higher federal excise taxes on diesel fuel compared to standard gasoline. The cost disparity between diesel fuel and gasoline is partly caused by additional federal and state taxes per gallon. Nevertheless, diesel fuel remains more affordable than petrol in many other countries, resulting in a larger population of diesel-powered passenger vehicles being utilized in Europe and Asia.
If a greater number of drivers in the United States were to switch to diesel-powered vehicles, it may have the potential to lower the price of diesel fuel. This could result in an increase in refineries manufacturing more diesel fuel and fueling stations providing competitive prices for both traditional diesel and eco-friendly bio-diesel. Volkswagen has consistently demonstrated its endorsement of diesel technology due to the advantages it offers in terms of performance and economics. However, starting from October, buyers will also be able to choose the 2013 Volkswagen Jetta Hybrid among other available options.
The Jetta Hybrid is a combination of a 1.4-liter, turbocharged and hybrid-assisted four-cylinder engine with a 7-speed dual-clutch DSG transmission, resulting in the production of 170 horsepower. This outperforms the Jetta TDI in terms of both performance and efficiency, as the latter is renowned for its fuel economy. The Jetta Hybrid has an estimated fuel efficiency rating of 30 mpg in urban areas and 42 mpg on highways, with a combined rating of 34 mpg (and potential for even more), thanks to its well-established technology. Could this mean that the Jetta TDI will become outdated? According to Volkswagen’s estimates, the Jetta Hybrid is expected to achieve an EPA rating of 45 mpg combined, surpassing its diesel-powered counterpart by an impressive margin of 11 mpg.
During the 2012 Detroit Auto Show, Volkswagen proudly announced that the electric range of the Diesel Jetta would surpass that of its diesel counterpart by a significant margin, offering a 1.2-mile electric range. Additionally, Volkswagen stated that the Jetta Hybrid would be competitively priced compared to other compact hybrids such as the Honda Civic Hybrid which is priced at $24,000. This suggests that the Jetta Hybrid will fall within a similar price range as the Toyota Prius C which is priced at $20,000, making it an attractive option for those considering purchasing the Jetta TDI priced at $22,990. As a result, these developments raise questions about how this will impact sales and adoption of the diesel-powered Jetta.
The TDI, weighing 3,161 lbs, is lighter than the hybrid counterpart which has a weight of approximately 3,300 lbs. This reduced weight potentially makes the TDI a more agile choice. Many loyal Volkswagen customers appreciate diesel engines for their performance and efficiency as they meet their needs. It is important to note that the EPA’s fuel efficiency ratings for the Jetta TDI are conservative. The diesel engine’s higher compression ratios and lean-burn combustion offer unparalleled efficiency when covering long distances at high speeds. Currently, no gas engine can match this level of efficiency without relying on an expensive hybrid system.
The average thermodynamic efficiency of diesel engines, which measures the work produced from fuel, is around 30 percent, significantly superior to gas engines. However, as emissions regulations become stricter, this lead is diminishing. Expensive after-treatment systems used for cleaning diesel exhausts also reduce efficiency. On the other hand, gas engines are consistently improving. Uwe Grebe, GM’s director of global advanced engineering, explains that while diesel engines will always maintain a slight advantage, the efficiency gap between gasoline and diesel engines will almost close within a decade. In the past ten years, technologies such as variable camshaft timing, direct fuel injection, and turbochargers have become common in spark-ignited engines. These technologies have been available for some time but advancements in electronics and materials have made them more widely adopted.
And there’s more on the way, like lean-burn combustion and homogeneous charge compression ignition (HCCI), a gas-combustion technology that blurs the line between gas and diesel engine cycles. Ricardo is working on a turbocharged engine that uses E85, a lofty compression ratio and high boost levels to achieve diesel-like efficiency. Rod Beazley, Ricardo’s VP of spark-ignited engines, boasts that“Ethanol-boosted concept engine achieves thermal efficiency in the low 40 percent range.” But don’t expect the diesel engine to lie down and play dead. We’ll continue to see incremental improvements in diesel efficiency,” says Marc Trahan, Audi’s North American director of quality and technology. “It won’t be as large as going from sequential port fuel injection to direct injection, but there are still more gains to be made.” Trahan says these smaller gains will come from hardware such as variable valve timing and independent cylinder combustion control, as well as improved after-treatment systems. Moreover, there are other factors in play.
According to GM’s Grebe, diesel fuel has approximately 14% more energy per volume than gasoline. This gives compression-ignition engines an advantage in terms of fuel economy, rather than thermal efficiency. However, everything could change if spark-ignited engines start using more energy-dense fuels. This competition is still ongoing. For instance, VW has implemented this in their golf with a 1. liter engine. It is suspected that this is for fuel efficiency without the delay of a turbo system. When turbo and supercharger are combined, it results in a small engine with good responsiveness at low speeds and decent horsepower at high speeds. The supercharger is turned off above around 3500rpm to prevent excessive fuel consumption, while the turbo continues to provide the necessary boost.
