Aug 10, 2007

Updated | Bajaj DTS-Si: My take

What is swirl?
Swirl, in the sense of combustion, is an effect that is usually engineered to act on the air-fuel mixture as it enters the combustion chamber. By a variety of means, the mixture is made to 'rotate' around the spark plug inside the chamber. Swirl is considered to be a good thing because it leads to turbulence.

What is turbulence?
Swirl is a pretty smooth looking thing (when you see false-colour velocity plots, that is), but like all things smooth, it does not last. As the piston comes up during the compression stroke, it breaks the swirl, officially called decay. When swirl decays, you get a random motion of the mixture called turbulence. Turbulence is good because it removes the opportunity for the air fuel mixture to separate and produce inefficient and variable (across cycles) combustion. Turbulence, and the great mixing of the air and fuel droplets also leads of fast burning, clean burning, and hence efficient flames. In essence, turbulence leads to cleaner, more complete combustion. In the context of engines, turbulence is a great asset at lower revs. Making the mixture swirl takes time, and reduces the amount of mixture you can pump into the chamber. So when revs come up, engine builders prefer smoother flows and higher volumes. In essence, if you wanted a superb high-rev punch in the motor, you'd be working towards greater flow rather than turbulence.

That's a comparison between the torque curves of the Platina and the well, Exceed (DTS-Si). See the massive extra torque available at low revs? That's the swirl effect, so to speak
That's a comparison between the power curves of the Platina and the well, Exceed (DTS-Si). See the extra power available at all revs? No replacement for displacement.
This curve was plotted by mounting the motor on a dyno and turning it over using a measurable force. The lower the force required, the less effort is needed to turn the engine over, meaning that friction losses are lower. The DTS-Si, as you can see, has a much lower curve.

What has Bajaj done?
Bajaj calls their new engine platform DTS-Si. DTS you know, Si is Swirl Induction. The company says DTSi, the Pulsar/Discover technology is evolving. The performance end of the evolution is DTS-Fi, which has debuted on the 220. The efficiency/economy end of that evolution will be held up by the DTS-Si engine.

Now stay with me. The old DTSi engine was simple. If you looked at the piston from the top down and marked the placement of the intake and exhaust valves and the two spark plugs, you would, more or less, get two lines perpendicular to each other. Think high flow, large bore, two quick burning flames. The DTS-Si offsets the valves and plugs. Instead of the two perpendicular lines, the valves and plugs 'alternate' in the four quadrants that the lines have dissected the circle into. The intake charge, therefore, enters the chamber, bounces off the bore wall and yes, swirls around.

Audi direct injection engine, FSI, uses an evolution of this. They inject the fuel directly into the chamber and the intake valve only lets in air. As the air swirls around the chamber, fuel is injected at the right time. At part loads (which is the majority of the time), the air is 'separated' into two layers. The layer around the spark plug is loaded with fuel and the outer layer is effectively 'dry.' When the plug fires, the outer air insulates the burning mixture reducing heat losses to the cylinder walls and reduces some of the overlap losses that happen from mixture escaping into the exhaust manifold while both the valves overlap.

That's the swirl part. Displacing 125cc, the motor is new from the ground up. Bajaj has made it really light (the 125cc motor is 1.5 kg lighter than the 100cc Platina engine and some 6 kg lighter than the 125cc Discover's) and use a number of ideas to reduce friction too. Think light, slippery motor. The motor's no economy-weenie either. While Bajaj do claim a substantial 9.5 bhp (that's more than all the 100cc bikes it will compete with and above or equal to most 125s as well), it also returns 109 kpl under standard test, which is 1 kpl more than the Platina. And Bajaj claim just over 1 kgm as the peak torque at 5,000 rpm which is impressive, especially when you see how far over the Platina torque curve this is, and how much the difference is.


This is a model of regular single-spark combustion


This is a model of DTS-Si combustion

What's the bike like?
The motorcycle will be called Exceed, although the exact spelling has yet to be announced. Xceed? EkSeed? I don't know. Like the engine, the bike will be sleek and light. Bajaj say that the low-end torque (14 kph is possible in top gear, it is said) makes the rideability stunning and all of those riders who like snicking into top gear early are going to be floored by the torque spread. Oh and this is not the Sonic.

This graph shows the evolution of the market share of 125+150cc segment and whatever's below that. Also, right at the bottom are the growth figures for April to July 2007, all together, 100cc and 125-150cc.
What's this mean to you?
When Bajaj said they wanted out of the 100cc game, they meant that they wanted the 100cc customer to have a more juicy alternative. 2 bhp more, more economy and similar price, in my book is juicy. Remains to be seen how more zing the styling will bring. The Exceed will be all new and probably be launched in September, first week would be my guess.

Bajaj say that while they sell 50,000 units of the Platina every month, the product basically breaks even and adds little or nothing to net revenue. Bajaj currently have nothing in what you call the top of the entry-level or bottom of the executive commuter segment and that's a crucial, crucial hole the Exceed will plug. The motorcycle will cost Bajaj roughly the same as the Platina to make, but will sell for approximately Rs 40,000 ex-showroom, which will mean the 6,500 extra bucks are pure profit and some taxes. Bajaj say that Discover 112 sales are pretty low, so any cannibalisation would be more or less ignored. Any upgrades from the Platina, obviously, will be welcome. The Exceed, if it proves popular and takes up substantial Platina sales, could replace the Platina.


Why is this bike significant?
Once more, Bajaj is taking the competition on by moving the playground. If all the claims come good, then once more, Bajaj will gained a couple of bike lengths by cleverly using technology. Swirl is not a new idea. But using it to produce a motorcycle that is defined by its economy is something no other Indian manufacturer has done. If the Exceed is successful, Bajaj will become less sensitive to the fickle entry level market. When sales cross 30,000 units, Bajaj say that the Exceed will also significantly boost market share. As Bajaj say, they are number two despite leading both the 125 and 150 segments (50 per cent market share across the segments!), and this is bike that they hope will fix the rest of the imbalance.

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14 comments:

Anonymous said...

Rearset, Nice review, as you said, if Bajaj delivers what it promises then the bike should b good. Platina ads. showed 108 kmpl, but one year old Platina rarely touches 60 kmpl. 125cc doing 60 kmpl is already there, Super splendor and Glam can do 60 kmpl in city sane driving. The graphs looks good on presentations, what matters is road !! CT100/Platina both failed promises of Bajaj. We should see how Si would perform !!

Siddharth Soni said...

I've been checking your blog regularly now. And this review makes me congratulate you. Great work. Am sure you are spending a lot of time on these articles.

Exceed seems a winner even before the game has begun. Styling is the last bit left to be known.

Anonymous said...

Article flows through nicely. Lucid style of article makes it easy to understand even for a layman. Coming to Bajaj, their strategy seems to be creating a new segment rather competing in the existing segments. If Exceed delivers, then surely Bajaj will become NO.1 bike maker in the country, there is no doubt about it.

first_synn said...

Say, any idea when they are gonna try their hands on the next flavor-of-the-month? You know, mating more than one cylinder on to a single crank and such....

100-125 whatever CC. Looks like lawnmower inc. is here to stay for a long long time.

Anonymous said...

Brilliant!.. sooooper.......

But why dont BAL invest some moola to provide a better gearbox. damn!

ruffrohit said...

hey! i must say, this is quite a commendable review and -if it turns out to be as you described- a very commendable bike too! though i wonder what became of the sonic???

anyways, i'm eagerly waiting for the launch now...

Anonymous said...

Contrary to your assumptions, swirl induction reduces turbulence! It makes for more disciplined movement of mixture inside cylinder. Injecting without swirl will cause more turbulence. Cheers.

rearset said...

It's not an assumption. Read the text again. Swirl decays into turbulence. This is an 'engineered' event. If there wasn't any swirl, there would still be turbulence, but it would be a more organic form of it, which would a)not be repeateable (the ability to repeat what happened in one cycle exactly and constantly is one of the major challenges of designing internal combustion engines) and b)not be as efficient (as in not tuned for maximum effect)

Nishanth said...

I agree with anonymous, and rearset your use of words like organic, repeatable and efficient is pure BS.

Get your basics right dude...turbulence is chaotic flow of fluids, swirl makes it more orderly.period.

rearset said...

Have it your way. I'm telling you what I know to be correct...

Anonymous said...

It sounds like it will have lot of vibrations like diesel engine?

rearset said...

Now why would you go and think that?

Tejas said...

I wanted a bike tht was cheap and wud take me frm point A to B, easy to maintain, decent power and give me good fuel economy...
XCD satisfied all of tht...
I did take the test drive and the engine felt smooth... smoother than any bike i have ridden till date...
and to my absolute surprise thr was absolutely no knockin! even @ 10kmph in 4th gear...
XCD will kill the market for its price...
i booked it for Rs.46,355 on road pune and is yet to arrive...
nice work on ur review...
keep it up!

Anonymous said...

I was impressed by Bajaj XCD. However one of my friends told me abt Honda Shine. I m very confused as looks wise i bilieve Shine is almost like Unicorn, however XCD does not look very attractive.
Can somebody help me out in deciding?