Tuesday, October 17, 2006

Which is Best: Diesel or Electric/Gas Hybrid?

diesel injection Diesel Engine or a Gas/Electric Hybrid? hybrid powertrain

The short answer to diesel versus hybrid is the choice depends on what you want to use the vehicle for. If you want a truck with lots of towing power, buy a diesel. If you want a fuel efficient commuter car for urban driving, buy a hybrid car like the Toyota Prius, or buy a turbo diesel-powered car like a VW.

Unfortunately, your purchase options are very limited because hybrid gas/electric powertrains and diesel engines are only available in a few cars. Diesels have long been a popular option in light trucks and the availability has been pretty good. But diesel cars have been in short supply – and will get even harder to find for the next year or so thanks to new emission regulations.

As usual we get the wrong regulations at the wrong time. The EPA decided it would be a good idea to require cars and light trucks with diesel engines to meet the same emission regulations as cars with gasoline engines. The Tier 2 emission regulations, which all cars must comply with start in 2007, require a fleet average of 0.05 grams per mile of oxides of nitrogen, a figure today’s diesels cannot meet without low sulfur fuel and electronic direct injection technology. The rules also limit particulate (soot) emissions, which requires diesels to have some type of particulate filter in the exhaust. To make matters worse, California, New York, Massachusetts, Vermont and Maine have all adopted even tougher diesel emission standards than the federal EPA standards.

In Europe, where gasoline costs several times as mucha s it does here, and where diesel emission regulations are less strict, diesel powered cars account for over HALF the car population. The European limits for oxides of nitrogen are EIGHT times higher.

Unless the new regulations are relaxes or repealed (fat chance for that happening), the diesel option in cars and some light trucks (depends on size & weight) will go away in 2007, and will only slowly return as the technology improves.

Diesel Options:

Currently, the only diesel-powered cars available are:

Mercedes E Class E320 CDI
Jeep Liberty CRD
VW Passat TDI
VW Touareg TDI
VW Turbo Diesel Golf TDI

Technical Differences: Diesel vs Hybrid Gas/Electric

The main attraction of a diesel engine is that it is more fuel efficient than a gasoline engine: up to 30% better fuel economy as a rule than a comparable gasoline engine of the same displacement.

A diesel engine uses high compression rather than spark ignition to burn the fuel. This eliminates the need for an ignition system (no spark plugs, coils or ignition module), but it does require a very high pressure fuel injection system, much higher than that on a gasoline engine. Most diesel engines have a glow plug system for cold starting. There is also no throttle on a diesel engine, so it sucks air more efficiently at idle and low rpm (reduced pumping losses). The trade off is that a lack of intake vacuum in the engine requires a separate vacuum pump for any vacuum operated accessories.

On diesel engines, fuel is injected directly into the combustion chamber as the piston approaches top dead center. The timing of the fuel injector is critical for good engine performance. Compression ratios are very high 18:1 or higher, so it takes a LOT of pressure (300 bar to 1800 bar) to inject the fuel into the cylinder or a precombustion chamber in the cylinder head. The heat of compression causes the fuel to ignite spontaneously. That’s why no spark plugs are needed.

Mechanically, a diesel engine is essentially the same as a gasoline engine except for the higher compression ratio. Diesels typically have stronger crankshafts, connecting rods and pistons than gasoline engines, and they typically run at lower rpms. Most of these engines are VERY durable and will last well beyond 150,000 miles with proper maintenance. Regular oil changes, however, are essential to maintain a diesel engine because they experience more blowby of combustion byproducts into the crankcase than gasoline engines.

Things that can go wrong with a diesel engine include injection pump problems, fuel injector problems, blown head gaskets, hard starting in cold weather if the glow plug system fails, and fuel waxing. Diesel fuel is actually a very light oil, so if it does not contain the right additives it can gel and plug up the fuel line or filter in cold weather.

Older diesels were also notorious for their idle clatter and black smoky exhaust. Many light truck diesel engines still have those attributes, but most of the direct injection passenger car diesel engines built by Volkswagen are relatively clean and quiet.

Would I buy a diesel powered car or truck? It would depend on the current price of diesel fuel versus gasoline, the cost difference to get the diesel option, and how much better fuel mileage the diesel gets over its gasoline counterpart. It would also depend on what I would be using the vehicle for (towing or general driving). Diesels do require a little more maintenance, and most owners who want to avoid cold weather starting problems are religious about using fuel additives in cold weather. I don’t see either of those things being a drawback if I wanted a diesel.

Hybrid Gas/Electric

Hybrid electric vehicles use a conventional gasoline engine for propulsion, and an electric motor for supplemental power. The gasoline engine turns an alternator that keeps a large high voltage battery charged. Some hybrids are designed to shut off the gas engine when the vehicle stops moving to conserve fuel. The electric motor is then used to accelerate the vehicle up to a certain speed at which point the gasoline engine restarts and takes over. For maximum acceleration, the electric motor and gas motor may both provide power to the wheels. How the vehicle is programmed to balance gas power and electric power affects overall fuel economy as do driving conditions. That’s why a vehicle like the Toyota Prius gets better mileage in stop-and-go city driving than it does on the highway.

On other hybrids, the electric motor is used more like a supplemental power source to boost acceleration when extra power is needed. This allows the use of a smaller, more fuel efficient gasoline engine that gets better fuel economy without sacrificing too much performance.

The third approach is to have a start/stop only system, where the engine shuts off when the vehicle is stopped, and automatically restarts when the driver steps on the gas pedal. There is no electric propulsion.

Hybrid Vehicles Currently Available:

Toyota Prius
Toyota Camry hybrid
Honda Accord hybrid
Honda Civic hybrid
Honda Insight
Lexus RX400H
Ford Escape hybrid
2007 Saturn Vue hybrid
2007 Mercury Mariner hybrid

Hybrid Complexity

A vehicle like the Toyota Prius is a technical marvel in my opinion. But it is also a VERY complex vehicle that is much more complex than any gasoline or diesel-powered vehicle. Consequently, the more complicated the system, the more stuff there is to go wrong.

As long as everything is working fine, I see no reason not to own a Toyota Prius or any other hybrid. But when these vehicles get some miles and age on them, I wonder how well they will hold up. Personally, I would NOT want to be the second or third owner of a used hybrid gas/electric vehicle. Why? Because of the high cost to replace the hybrid high voltage battery, because of the high cost to fix any electrical quirks or failures that may occur in the powertrain, and because replacement parts are NOT yet available in the aftermarket for these vehicles. New car dealers currently have a monopoly on these cars, and charge accordingly for parts and service. Most independent repair shops and garages are not yet up to speed on hybrid technology, so the new car dealer is about the only place you can take your hybrid if the electronic components or battery need repair. Ordinary stuff like brakes, tires, mufflers, cooling system, or the gasoline engine can be serviced anywhere.

The next-generation hybrids that will have a plug-in option and larger battery so the vehicle can operate more on electric power and less on gasoline power will make hybrids even better.

Diesels are Better

In the meantime, I see clean direct injection diesels as the better short-term technology. The EPA needs to cut us some slack and roll back the new Tier 2 emission requirements for diesel engines. The environmentally-sensitive Europeans do not seem to be overly concerned about current diesel emissions, and are way ahead of us in diesel technology.

Diesel Sets New Land Speed Record

diesel race car Who says diesels have to be slow?

On August 22, 2006, the JCB DIESELMAX set a new land speed record for diesel-powered vehicles with a speed of 328.767 mph at the Bonneville Salt Flats, Utah. Powered by two state-of-the-art JCB444-LSR engines developed by Ricardo, the JCB DIESELMAX beat the existing record by almost 100 mph. The race car was powered by two JCB444-LSR engines with two-stage inter-cooled turbo-charging, high pressure fuel injection and a low compression ratio, low temperature combustion system. All of these technologies are being developed by Ricardo for application on the high performance, ultra-low Tier II emissions diesel vehicles of the future.

EV1 electric car Electric Cars are Best

Long term, the best powertrain choice in my opinion is a pure electric vehicle. Electric vehicles are environmentally clean, quiet and energy efficient. Fuel costs are potentially equivalent to over 100 mpg at today’s energy prices. If charged by electricity from cheap wind, hydroelectric or nuclear power sources, the economics make even more sense.

The battery technology isn’t quite there yet for a do-everything electric car, but ni-cad and lithium ion batteries are more than adequate for urban commuting, which satisfies the needs of about 90% of the population today. The problem is getting the major auto makers to commit to electric cars.

It’s no secret that car makers do NOT want to build electric cars. Why? Because electric cars are not profitable (at least not yet). Development costs are high, battery technology is still iffy, and the domestic car companies are heavily invested in internal combustion engine technology and production tooling. They would much rather sell us accessory laden SUVs and luxury cars than small fuel efficient vehicles regardless of what kind of power system is under the hood.

The domestic car companies cite all kinds of statistics that claim nobody wants electric cars, nobody would drive them if they were available other than wealthy left wing liberal Hollywood celebrities, and they would be too expensive for the average schmuck. Proponents of electric cars say the cars make perfect sense, that people would be standing in line to buy them if they were readily available, and that electric cars could be both affordable and practical if mass produced by major auto makers. I agree.

Related Articles:

Who Killed GM's EV1 Electric Car?
Light-Duty Diesel Diagnosis
About Alternative Fuels
E85 Ethanol Alcohol Alternative Fuel

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