Design News for Mechanical and Design Engineers

Diesels King of the Hill

• Because diesel engines are built to withstand high compression and combustion, they're intrinsically stronger, enhancing engine life. Diesel fuel is actually an oil. Its lubricating properties aid engine life.
• One drawback to diesel operation is in refueling. Because the fuel is oily, it doesn't evaporate like gasoline and when it gets on your hands, it's a stinky mess.
• Finally, diesel engines are easy to "soup up." With a fueling computer, bigger injectors, and a larger turbo, I can easily double my horsepower output and raise the torque into the high three digits for a few thousand dollars. So I have to give a little smirk when I see guys (and gals) tooling around thinking they're King of the Hill in their V-10s and "Hemi's." My diesel can outpull them and walk away from them in acceleration, and I'm getting nearly double the fuel mileage while doing it too!

Tom Hybiske, Framingham, MA

Thanks for the article, reaffirming what I have been saying about diesels for over a decade now, but I am confused. Why are American automakers always late to the party, and never learn from the competition? I also do not understand why you hardly mention two manufacturers that have had a high percentage of their vehicles equipped with clean burning diesels. VW has one of the best diesel engines around (the 1.9l TDI), as shown by getting a Ward's 10-best engine award, the first ever for a diesel. My 1997 Passat TDI gave me 54-56 mpg year-round. Mercedes has had a diesel engine available since the 60s. As a matter of fact, when GM destroyed the possibility of diesels being big here 20-some years ago, 80% of all Mercedes sold in the US were diesel.

Mike Roberts, Milton, WI

I enjoyed Larry Zirkle's article on corked bats (DN 09.08.03). It reminded me of a longstanding argument between my brother-in-law and me that I think he might be able to settle: All things being equal (bat speed, bat weight and impact location), will a batted ball go further when the incoming pitch is 70 mph versus 95 mph? He contends that the energy of the incoming pitch will cause more of a "rebound effect" and therefore result in a further hit ball. My point is that the faster thrown ball has more energy to overcome, therefore the faster pitched ball will not fly as far. A steak dinner is riding on your response.

Jayson Thorp, Design News reader

Zirkle's response: Generally speaking, your brother-in-law is right. For example, if you throw a ball against a concrete floor, the harder you throw it, the higher it will bounce. The rebound speed depends on the coefficient of restitution between the surface of the ball and the concrete surface, but always increases if the thrown speed increases. Increased thrown energy means the rebound energy will be higher. However, for a bat and ball the rebound speed of the ball could be either increased or decreased depending on the coefficient of restitution (e), the mass of the ball (M _ball ) and the mass of the bat (M _bat ). If we simplify and consider the bat to be a point mass, the result depends on the factor e(M _bat /M _ball ). If this factor is greater than 1, the rebound speed increases with increased thrown speed. If this factor is less than 1, the opposite occurs. Since normal values for these variables are in the vicinity of e = 0.55, M _ball = 5.1 oz, M _bat = 30 oz, the critical factor has a value of 3.23, indicating that the rebound speed will increase with thrown speed. Of course, if you had a non-standard bat of light weight and a non-standard ball of large weight, the critical factor could become less than 1, and the rebound speed would be reduced with increased ball speed. A bat with distributed weight is a little more complicated, but the general principle would be the same. Since you are both somewhat right (and somewhat wrong), I guess I get the steak!