Column: Spark Plugs – Who Needs Them?

Interesting | January 7th, 2010 by 22
bmw 6 cylinder diesel engine 750x500

There are moments of clarity in life when you realize that some things you were reliant upon are no longer needed. Take for instance, the …

There are moments of clarity in life when you realize that some things you were reliant upon are no longer needed.
Take for instance, the ‘Thigh Master.’ Popularized in America during the 1990’s, infomercials went on the offensive, claiming that the Thigh Master was an essential part of any workout routine. While in some households the Thigh Master was used religiously for years; the dawn of this millennium has shown that a far better workout can be accomplished using superior equipment at your local Gym. (Youtube Link)

It seems we’ve also been convinced that spark plugs are an essential part of our car’s engine. From the very beginning, spark plugs have been commonplace in automotive engines. Varying by design, some have incorporated exotic metals such as iridium and platinum, but ultimately – they create a spark for combustion as they always have.

BMW Blog   Spark Plug 655x325

Modern demands for increasingly efficient and environmentally friendly engines have given us pause for a moment of clarity. Advancements must be made in the design of internal combustion engines to keep in step with ever-higher fuel efficiency and emissions standards. Is it possible that someone could invent a new form of internal combustion, one that proves itself powerful and refined while extremely fuel-efficient?

Enter Rudolf Diesel.

Born in 1858 of Bavarian descent, Rudolf became a Refrigerator Engineer (cutting edge at the time, mind you), but his secret love was in engine design. Drawing upon his education from Munich Polytechnic, Rudolf set about on a special project; sketches, calculations and drawings accumulated before him. On August 10th 1893, Rudolf had completed his first working prototype: a single cylinder engine standing 3 meters (10ft) tall with a large flywheel at its base. That very day the giant engine roared to life, only Rudolf’s heart beating heavier and louder than his invention before him. The first revolutions of this engine had shown the world that fuel could be ignited without a spark. A year later Rudolf went on to patent his invention, proudly coining it the ‘Diesel’ engine.

By the early 1900’s Diesels started to show up in many engine applications from agriculture to marine use, transportation to factory power generation. In modern times there are diesels flying above in airplanes, powering small pumps and generators around construction sites, and powering the largest of ships and locomotives. Diesels are found globally in many places and of course, under the bonnets of our beloved BMWs.

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BMW’s use of Diesel engine design stretches back to their history in aviation. In 1935 BMW developed a prototype Diesel Aircraft Engine, the BMW 114. The 114 was a 9 cylinder air-cooled radial engine displacing 27.7 Liters. No doubt smoothness and lightweight construction were hallmarks of this first BMW Diesel considering its application. Years later the same hallmarks of engineering are found in BMW’s diesel engines; only smoother, lighter and drastically more powerful. Oh, and a little bit smaller.

So how does it all work? Let’s get this Diesel spinning…

In its most simplistic form, a Diesel engine transforms the potential chemical energy of fuel into kinetic energy through ‘internal combustion’ (controlled explosions), as does any gasoline-fueled engine. The difference lies with its ignition.
Since the late 1800’s, internal combustion engines burning petroleum-based fuels used an electric spark to ignite the air-fuel mixer contained within. To this day the same basic concept of ignition is used, igniting the compressed air-fuel mixer with an electric spark generated by a spark plug.

Diesels differ in concept by igniting the air-fuel mixer without the use of sparkplugs. How is this possible, and what Law of physics did Rudolf Diesel contemplate when designing the Diesel engine?
French Chemist Joseph Louis Gay-Lussac made a discovery in 1802 that was later fundamental to the design of Rudolf’s engine. Gay-Lussac discovered a relationship between the temperature and pressure of a gas, where the temperature of a gas will increase as the pressure of this gas is increased, the volume remaining constant. Rudolf went on to determine that if he could compress a fixed volume of air to a high enough pressure within the cylinder of his engine, it’s temperature would increase to the point of ignition.

He was right.

This explains the high compression ratio of a diesel engine, literally squeezing the air-fuel mixer to such a high pressure and temperature that the fuel ignites. Consider the compression ratio of the BMW 335d’s Diesel engine at 16.5:1. That is to say that in ratio, this engine takes 16.5 Liters of air and compresses it into 1 Liter of space. This also explains why traditionally Diesel engines have been heavier, the walls of the block made thicker to withstand the force of compression.

Prodigious Power, Torque & Refinement – No Spark Plugs Required


Advancements in Diesel technology have transformed what were once rough running, loud and odor emitting engines into smooth, quiet engines barely emitting a scent.
Time does not permit us to consider all of BMW’s advanced Diesel technologies in depth, but lets take a brief look at a few highlights:

Advanced Turbo Technology. The use of Variable Twin Turbos has reduced turbo lag to a thing of the past and elevated performance to levels only a sports car could claim. For an in-depth consideration of BMW’s incredible Turbo technology, please hit the jump.

Direct Fuel Injection. First used in 1998, this significantly improved the efficiency and responsiveness of BMW’s Diesel engines – developing their sporting character. This technology also paid huge dividends in refinement, increasing smoothness and reducing noise levels of the engine.

Common Rail Fuel Injection. BMW has gone to great lengths to advance this technology, and are in fact leaders in the field. Common Rail Fuel Injection facilitates highly accurate fuel metering under extremely high pressures prior to injection (the latest BMW engines are injecting fuel at over 2000 BAR/29,000 PSI!). Along with the use of precision Piezo injectors, fuel is atomized and distributed for complete combustion; every droplet of fuel is translated into stump-pulling power and torque.


Diesel Particulates Filter. This technology allows for reduced emissions and the elimination of “Soot” from the exhaust. The filter unit is mounted directly on the exhaust manifold and is self-cleaning as it incinerates the particles is captures; it is 100% maintenance free.

Blue Performance Urea Injection. To nearly eliminate harmful Nitric Oxide emissions, BMW has developed a system whereby urea is injected as a catalyst to eliminate NOX in the exhaust system. The by-products are Nitrogen and water vapor, both harmless to the environment.

Aluminum Alloy Construction. The greatest adversary of a BMW performance car is weight. As mentioned earlier, Diesel engines are traditionally built heavier to withstand the higher operating forces within. The consequence of this weight penalty has always been severe – but BMW has applied their lightweight design philosophy to their Diesel lineup, and the results should have gasoline engines running for cover. BMW’s latest diesels use Aluminum Alloy for the construction of the engine block, and crankcase. On the latest 3 series, a negligible weight penalty of 150lb is added moving from the 335i to the 335d – a remarkable achievement.
There are many, many more technologies beyond those mentioned, but the message is clear: BMW has advanced the performance envelope of Diesel engines far beyond what was ever thought possible. And the best is yet to come.

Diesel power offers a new interpretation of the Ultimate Driving Machine


BMW Motorsport plays its role in making Diesel Racing history. In the 1998 running of Le Mans, the checkered flag fell to the blur of a BMW 320d completing its final lap of the illustrious race. BMW went on to achieve great success in racing high-output Diesel engines. Stunning victories followed in the 2003 and 2004 Paris-Dakar Rally; A Twin-Turbo Diesel BMW X5 took both Checkered Flags and was the first Diesel in history to win a special stage. Audi’s success in LeMans racing gives further credence to the legitimacy of Diesel race cars.

Diesel ///M?

M emblem
The Vision Concept’s 3 cylinder Diesel is a technological masterpiece, and gives us a glimpse into the possible future of ///M road cars. The potent 1.5 L engine is currently the world’s most powerful Diesel relative to its specific output of 109 hp/Liter. The mighty Diesel also produces a massive 214 lb-ft of torque flat across its powerband. Applying the Vision Concept’s specific-output to the 3.0 Liter in the 335d would produce 326 hp! Consider that the E46 M3 produced 333 hp from a 3.2 liter, and the implications make our right foot very excited.


Diesel powered BMWs are not something to be scoffed at or dismissed. The unique drive characteristics of Diesel engines unleash new possibilities for what constitutes the Ultimate Driving Machine. Endless torque at all RPM; a brilliant rumble that tickles your ears and makes grown men giggle; scorching performance from high-output engines touting horsepower figures fit for the racetrack; lightweight construction that lends itself to perfect balance – begging you to carve the next corner. All while achieving phenomenal fuel mileage and efficiency, leaving the smallest imprint on the environment possible. I’m convinced that the sporting, torquey character of BMW performance Diesels should be embraced by all who love tail-out antics. The dawn of a new age of performance cars has arrived, and you can rest assured that BMW is the undisputed leader in advancing efficient, dynamic motoring.

So is there anything negative we can say about Diesels after a thorough evaluation?

Well, on the down side, Diesels have proven more expensive to manufacture since all engine components must be fortified to survive the extremely high pressures within. Of course, this also plays out as a positive factor since the robust design renders a Diesel very reliable, durable, and long lasting. Also of some concern is the lower redline of Diesel engines. As a true enthusiast of high revving engines, I admit this is a drawback for the time being. Through design, a very balanced Diesel will be able to rev well beyond the typical 5,000 RPM limit, and in time we will see higher revving diesels. Of some consolation however, is the usable powerband. With 442 lb-ft of torque on tap from 1,500 RPM on the 3.0 L TwinPower Turbo Diesel, the powerband is simply moved lower in the rev range. Picture it as though the bottom 4,000 RPM have been cut out of your S54 M3 engine; your car now idles at 4,000 RPM. Now add 190 lb-ft of torque.

This kind of thrust will make you wish for every green light to turn red.

Maybe it’s time to pull the spark plugs out of your car and find a place for them beside the Thigh Master on that dusty shelf in your garage. To those of you still on the fence about Diesels or to those who claim Diesels are dirty, please read the following sentence very carefully.

The only smoke trailing a BMW Diesel is swirling off its tires.

22 responses to “Column: Spark Plugs – Who Needs Them?”

  1. Doug says:

    First off, nice article, it was an enoyable read, Shawn.

    However, Having complimented you thus on your research and presentation, and given that this is a position piece, *I* do need to scoff and dismiss diesels :). Diesels are fantastic for acceleration + fuel economy as you’ve well laid-out. However, I think many [others] will agree that they are not nearly as fun to drive, as they seriously lack power and exhaust note that’s gained through high rpm. While the high torque gives you good acceleration through the bottom end (and lower speeds), the power doesn’t build enough to overcome the exponentially increasing resistance. Charging ahead in a gas engine has a building crescendo of power, noise *and* acceleration (and endorphins) at the top end that the diesel simply lacks.

    Btw, the Thighmaster CAN and DOES replace an entire fitness regimen. There’s no other way to eat 50 pork sausages a day and still be as svelte as me. I am living proof.

    Getting into metaphors, I think gunning a good gas (preferably NA) engine is like the courting game with a beautiful, tall, intelligent woman, a battle of wits building the suspense and anticipation towards a night at the St. James. A diesel, on the other hand, is like meeting a short, pudgy girl with a suspiciously deep voice at a truck stop and having an abrupt copulation at the super-8 across the street.

    Say YES to spark plugs!

  2. Bert says:

    While I am a big fan of diesels, I still prefer petrol engines. There is nothing better than the rumble of an American V8, or the raspy exhaust note from an E46 M3.

  3. Pavel says:

    I too like very much BMW petrol engines. However, I have driven the new 530d GT and I have to admit that the new engine and transmission is brilliant. I have driven many diesel cars where owners said “you almost do not recognize it’s not diesel”. There always was that “almost”… But not THIS time. This engine had me converted…

  4. Horatiu B. says:

    Shawn, great article. :) Enough said.

  5. joe says:

    cars will soon be so quite they will have to produce their own artificial sounds to make driving excating again :)

  6. Mike says:

    I drove a 535d for two weeks across Germany/Austria on vacation last year. I came back SOLD on diesel performance! I must say that I’ve been disappointed with BMW’s marketing of this engine in America; they’ve really kept it under the radar. However, potential buyers need to give this engine a try…….. they will be amazed!

  7. DougC says:

    I considered a diesel briefly last spring when I bought my 335i, but the deal-breaker was the lack of manual transmission option. No one at BMW I asked knew why. My guess was that the extra low-end torque would be too much for a clutch. Any other ideas?

    • Doug says:

      Did they offer a 6-speed auto on the diesel, or just a 7/8 speed auto? Maybe the limited RPM range needs more gearing.

    • BMW doesn’t have a manual gearbox that can handle the torque of that particular diesel engine. It’s not so much about the peak output, but how it’s applied as well.

      • Doug says:

        I was just digging at whether it was actually a question of gearing, since they don’t make a 7 or 8 speed manual. 35mpg is good but not spectacular (like the 4-cyl diesels), so they may not have wanted to undermine that (or performance) with a 6-speed.

        The torque might be too much, but did they really not have a more robust MT available? Does BMW make, procure (OTS) or outsource their transmissions?

  8. Blaze says:

    Great Article.

    Just one question…I had the (may be incorrect) impression that they couldn’t use Aluminum in diesel engines because the diesel was corrosive to the aluminum, that’s why they used steel all these years. Is that impression incorrect, or has BMW made some developments with their alloys?

    • atr_hugo says:

      Aluminum and diesel fuel coexist AFAIK (and marine applications store diesel fuel in aluminum tanks, WIW) – big problem is strength and most manufacturers defaulted to iron alloys to solve that problem.

  9. atr_hugo says:

    Great article Shawn!

    If youse guys haven’t driven a 335d, lean on your CA and beg a drive. Other than a bit more vibration at idle, this will be hard to distinguish from a gas inline 6. Granted the thing shifts at 4200, but around town (or at cruising speed) it is as effective as a gas motor. And if it’s to be a highway car, this thing has extremely LONG legs (~ 580 mile range per tank).

    A couple of caveats, diesels don’t employ throttles so there is no engine braking to speak of (and the BMW diesels don’t use ‘Jake Brakes’ ;-). Also, RPM is limited to the burn rate of the fuel. Diesel is slower to burn than modern gasoline; even the LeMans Audis max out around 5K RPM.

  10. Andrew says:

    I have a BMW 123d Coupe and it is amazing. So much torque I can easily wheelspin in 1st and 2nd gear. If the roads are damp it will even wheelspin in 3rd if I put my foot down a bit hard. Keeps the traction control busy.

    And this twin turbo diesel has a great engine note. As it approaches the redline of around 6k it seriously sounds like a rorty 4 cylinder petrol. It’s amazing fun to drive fast on twisty roads.

    And I’m averaging under 6l/100km… (over 40MPG)

  11. Keith says:

    Hi All,

    Just read the article and the comments posted, well what can I say its a very good article and I do acknowledge the comments of those petrol v8/v10 sound tracks. But I can tell you by the experiance of owning a 535d 272bhp msport. This diedel car is amazing, I have owned her now for 4 years and I still love the experiance of driving her. One thing the BMW diesel engines have over most petrol is the scope to increase performance for little expence.

    I have the blufin remap from superchips that increases bhp to 340 and give over 500 ft of torque, add the k&n airfilter and its pushing close to 350bhp, fuel enconomy is better, I get over 40 mpg to the gallon on a decent run. She excelerates 0 to 60 in 5.1 seconds and tops out at 174mph, and getting there doesnt take long. The power is relentless and smooth, and if the roads are wet the traction stability lights come on at over a 100mph as the power being delivered is so vast, thus it only being available in the auto as the manual gearbox would just get ripped to pieces.

    I agree its not an M5, but your lucky to see 16mpg in one of these and if you look at the states for every day driving you cant get much better for your pound. I know ive mentioned the performance states here quite a bit, but mostly this drives so smooth and is the best day to day car ive owned, and remeber this isnt a super car and can carry 5 people in comfort. The other thing, she has done nearly 90,000 miles and hasnt missed a beat, and oil changes come around every 19,000 making it a lot cheaper than most petrols during your ownership.

    Anyway, sorry for the large post – but I thought I would share my experiance with you as this is an amazing engine.

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